Home

Mechanical ventilation - PACT

1. A All things considered you opt to increase the FiO LEARNING ISSUES Management of oxygenation De escalation and weaning Note ie severely hypoxaemic patients a major reduction in PEEP should be avoided You maintain sedation and paralysis and change the mode to PCV with a frequency of 13 bpm and I E 1 3 6 You maintain PEEP at 8 cmH 0O while increasing the FiO to 0 8 You adjust the above PEEP inspiratory pressure Pcontr to 18 cmH 0 to achieve a Vt of 770 ml Ppeak is 28 cmH30 71 Patient Challenges Noe SNA you choose PCV for passive ventilation first decide your tidal volume target and then adjust the inspiratory pressure to achieve this tidal volume With several dual control modes of ventilation this latter task is automatically performed by the ventilator A double occlusion manoeuvre shows an inspiratory pause pressure of 26 cmHs0 and a PEEPtot of 9 7 cmHs0 PEEP is 1 7 cmHs0 ABGs reveal pH of 7 30 PaCO of 50 mmHg 6 6 kPa and PaO of 52 mmHg 6 8 kPa Haemodynamics are stable 2 a Volume ml 01213145 6 F 8 8 WHR 4 iS b if 8 1 wo seconds LEARNING SSUES Inspiration Volume control vs pressure control Q Give arguments as to why you think some of the new ventilator settings are safe and effective and others are not A The new settings have been effective in reducing dynamic hyperinflation and improving PaCO and pH Ppeak is acceptable considering tha
2. PATIENT CENTRED P f AA ACUTE CARE TRAINING AN ESICM MULTIDISCIPLINARY DISTANCE LEARNING PROGRAMME FOR INTENSIVE CARE TRAINING Mechanical ventilation Update 2011 eee Update 2011 Module Author Update 2011 Nicol PATRONITI Department of Experimental Medicine University of Milano Bicocca Ospedale San Gerardo Nuovo dei Tintori Monza Italy Module Author first edition Giorgio Antonio IOTII Anestesia e Rianimazione II Fondazione IRCCS Policlinico S Matteo Pavia Italy Module Reviewers Anders Larsson Antonio Pesenti Janice Zimmerman Section Editor Anders Larsson EUROPEAN SOCIETY OF INTENSIVE CARE MEDICINE Mechanical ventilation Update 2011 Editor in Chief Deputy Editor in Chief Medical Copy editor Self assessment Author Editorial Manager Business Manager Chair of Education and Training Committee Dermot Phelan Intensive Care Dept Mater Hospital University College Dublin Ireland Francesca Rubulotta Imperial College Charing Cross Hospital London UK Charles Hinds Barts and The London School of Medicine and Dentistry Hans Flaatten Bergen Norway Kathleen Brown Triwords Limited Tayport UK Estelle Flament ESICM Brussels Belgium Marco Maggiorini Zurich Switzerland PACT Editorial Board Editor in Chief Deputy Editor in Chief Respiratory failure Cardiovascular critical care Neuro critical care and Emergency medicine HSRO TAHI Obstetric critica
3. s condition is closely monitored and the clinical team is ready to progress to tracheal intubation at any time The non invasive approach often continuous positive airway pressure CPAP initially will often progress to early initiation of mechanical respiratory support which is most likely to be effective when mechanical support is needed for just a few hours rapidly reversible cardiogenic lung oedema is a typical example or when it is applied only intermittently In other cases deteriorating lung function will necessitate tracheal intubation Later non invasive ventilation can be reconsidered to assist weaning of an intubated patient thus allowing earlier extubation Planned NIMV immediately after extubation in patients with hypercapnic respiratory disease has been shown to improve outcome see reference below es Ferrer M Sellar s J Valencia M Carrillo A Gonzalez G Badia JR et al Non invasive ventilation after extubation in hypercapnic patients with chronic respiratory disorders randomised controlled trial Lancet 2009 374 9695 1082 1088 PMID 19682735 5 Task 2 Initiating and de escalating mechanical ventilation ARF WITH CRITERIA FOR VENTILATORY SUPPORT Criteria for intubation failure success FULL SPONTANEOUS BREATHING Decision making between invasive and non invasive ventilation NIMV at different stages of patient s course For general information about non invasive ventil
4. Inspiratory dynamic End inspiratory static End expiratory dynamic End expiratory static Maximum pressure applied by the ventilator Maximum stress on the large airways Maximum pressure distending the respiratory system Maximum stress on the alveoli Baseline pressure applied by the ventilator external PEEP It artificially increases the end expiratory lung volume Minimum pressure distending the respiratory system intrapulmonary PEEP It is the true determinant of the end expiratory lung volume 50 CLINICAL MEANING Risk factor of tracheo bronchial barotrauma It opens collapsed alveoli but it is also a risk factor of alveolar barotrauma It keeps the alveoli open but it may adversely affect haemodynamics It keeps the alveoli open but it may adversely affect haemodynamics Task 4 General working principles of positive pressure ventilators Types of airway pressure For bedside measurements of respiratory mechanics consult the reference below es Iotti GA Braschi A Measurements of respiratory mechanics during mechanical ventilation Rhazuns Switzerland Hamilton Medical Scientific Library 1999 ISBN 3962186503 Graphic monitoring of expiratory flow provides important qualitative information about airway obstruction and dynamic pulmonary hyperinflation A With the interactive tool Virtual MV Appendix you can simulate different patients and learn to perform manual calcul
5. and the flexible connector for the tracheal tube are normally replaced every day or more frequently when macroscopically contaminated Ventilator maintenance The maintenance of modern ventilators is simple A user s tasks are normally limited to e Replacement of the external circuit e Cleaning and disinfection of some parts of the internal expiratory line e Replacement of the oxygen cell when exhausted e Simple calibration procedures and tests 47 Task 4 General working principles of positive pressure ventilators Preventive maintenance must also be performed by trained technicians according to a specific schedule o Have you ever read Every ventilator is to be set up and maintained according to the users manual of specific procedures well described in the user manual your ventilators THINK Different models of ventilators have similarities but also important differences Never forget that safe and effective application of mechanical ventilation implies knowledge about the specific ventilator you are using You should read the users manuals of your ventilators and consult the manuals when in doubt Studying the manuals is a necessary step frequently neglected to maximally exploit the features of your ventilators Most likely you will discover functions you did not even know existed Ventilator monitor Airway pressures and flow are the signals on which the entire monitoring system is based For
6. because any ventilation induced increase in right heart response to afterload could increase the shunt and worsen oxygenation PERS Rea Assist respiratory muscle activity With appropriate settings the ventilator can generate an increase in the airway opening positive pressure synchronised with the action of the inspiratory muscles thus working as an external mechanical assistant of the inspiratory muscles The physiological response to external assistance is an increase in tidal 26 Task 3 Underlying physiological principles guiding mechanical ventilation volume coupled with a decrease in respiratory drive and activity resulting in lower respiratory frequency and lower amplitude of the contraction of the inspiratory muscles Different modes of assisted mechanical ventilation can be used to support the patient s respiratory effort e PSV delivers the designated support the set level of pressure support independently from the patient effort e Proportional Assist Ventilation PAV and Neurally Adjusted Ventilatory Assist NAVA adjust moment to moment the level of assistance to the patient effort The greater the patient effort the higher the level of assistance and vice versa e The volume based ventilatory modes decrease the level of assistance as patient effort increases 2500 2000 1500 N 1 1000 1 2 e n 3 _ m 11 4 500 eeeen 5 amp n 6 oll gt scadh 1 7 1 8
7. o o 10 Psupport cmH 30 This graph shows how eight different patients with acute respiratory failure responded to stepwise increases in pressure support level Each one of the patients decreased their spontaneous inspiratory activity expressed on the x axis as work of breathing Q In the graph above the same pressure support level of 24 cmH20 is associated with a totally different spontaneous inspiratory activity in patients 4 5 6 and 7 with work of breathing ranging from a below normal value in patient 4 to an extremely high value in patient 7 Give reasons for this A These four patients must have different ventilatory loads because of differences in compliance and or airway resistance and or intrinsic PEEP and or different alveolar ventilation requirements Ideally the mechanical support should be individually tailored to each patient The patient s response to an increase or decrease in ventilator support is usually quite rapid and a new steady state can be reached within minutes Setting the 27 Task 3 Underlying physiological principles guiding mechanical ventilation ventilator to assist the respiratory muscles is a process of trial and error requiring e Formulation of targets and e Assessment of results Q A non sedated neurologically intact patient is assisted with Pressure Support Ventilation PSV and exhibits an irregular breathing pattern Periods with large Vt are alternated with per
8. 13 5kPa but of the patient Although a PaO of 80 mmHg 11 kPa always a remains a desirable goal the target can be decreased to 60 point falls mmHg 8 kPa or probably even lower when hypoxaemia is progressively more refractory to treatment and the risk of ventilation related with age adverse effect is higher Impaired oxygenation is the main problem in lung failure it may be a consequence of six possible mechanisms e Low FiOz due for example to altitude aa aa Hypoventilation especially when breathing low FiO targets for pH e Impaired pulmonary diffusion capacity rarely a cause and PaCO of hypoxaemia e Ventilation perfusion V Q mismatch e Shunt due to perfusion of non ventilated lung regions e Desaturation of mixed venous blood if combined with shunt or V Q imbalance es Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 199 202 Oxygen therapy 19 Task 3 Underlying physiological principles guiding mechanical ventilation Fink M P Abraham E Vincent J L and Kochanek P M editors Textbook of Critical Care 5th Edn Elsevier Saunders Philadelphia USA 2005 p 454 457 See also the PACT module on Acute respiratory failure Inhaled oxygen Hypoxaemia due to V Q mismatch can be effectively counteracted by increasing the inspired oxygen fraction FiO2 The limit to using high FiO is imposed by oxygen toxicity In general we
9. 172 173 Mechanical ventilation with low tidal volumes 228 230 Respiratory support The acute respiratory distress syndrome network Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome NEJM 2000 Vol 342 No 18 1301 1308 Management of CO elimination alveolar In gee a PH i 140 minimum limit o ventilation 7 25 1s considered safe but PaCO2 and pH targets permissive targets for pH and PaCo The ideal target for pH is easy to define corresponding to should be normal pH in most cases In some instances a compromise individually between tidal volume reduction strategy and a lower pH level chosen according to the general state of the patient needs to be achieved 13 Task 3 Underlying physiological principles guiding mechanical ventilation The ideal target for PaCO varies depending on e Metabolic side of the acid base balance and hence pH e Usual PaCOsz levels of the patient e Possible therapeutic need for moderate hypocapnia In severe restrictive or obstructive lung disease aiming at normal value targets for pH and PaCOz may be incompatible with the mechanical safety of ventilation In these cases less ambitious targets will likely be required involving permissive hypercapnia and acidaemia Alveolar ventilation and minute ventilation See Charles Gomersall video on applied respiratory
10. 2 Initiating and de escalating mechanical ventilation Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 184 186 Tracheal intubation See also the PACT module on Airway management Non invasive mechanical ventilation NIMV When effective it may be associated with a better outcome but switching to the invasive approach will often be necessary 1N Safe and effective management of mask ventilation requires At least some residual spontaneous breathing the need for full mechanical support is an absolute contraindication to a non invasive approach No anticipation that high levels of positive pressure being required Ability to tolerate temporary disconnection from the ventilator Haemodynamic stability Co operative patient The ability of the patient to protect their own airway No acute facial trauma basal skull fracture or recent digestive tract surgery b When assessing your next ten patients with acute respiratory failure requiring mechanical support consider the question is the need for the tracheal tube merely to be an interface with the mechanical ventilator If the answer is yes check whether all the requirements for mask ventilation are fulfilled and discuss with colleagues whether non invasive ventilation might be better used as the initial approach CEG Mask ventilation is often a reasonable initial approach as long as the patient
11. D Airway Pressure Release Ventilation is an extreme concept of BIPAP with a very short low pressure phase 54 Self assessment 7 When a Heat and Moisture Exchanger HME is utilised during IPPV it A Must be mounted in the inspiratory line to be efficient B Will increase apparatus resistance C Should be avoided removed in patients with severe impairment of COs elimination D Will have no influence on apparatus deadspace 8 Ventilation induced lung injury may be minimised by the following A Volume controlled ventilation mode B Tidal Volume restriction to 6 ml kg C Limit plateau pressure below 30 cm H2O D Limitation of PEEP below 5 cm H2O 9 Regarding the I E ratio A Is normal set between 1 3 and 1 4 B Should be lowered to decrease intrinsic PEEP C Increase I E ratio may improve alveolar recruitment and oxygenation in ARDS D Adjustment of I E ratio must be matched with respiratory frequency 10 The effects of PEEP on improved oxygenation can be explained by A Re opening of collapsed alveoli B Increased FiO C Increased functional residual capacity D Decreased static compliance 11 Various methods to set optimal PEEP at the bedside include A Arterial PaOs B Analysis of the pressure volume curve lower inflection point C Recording of the oesophageal pressure to estimate transpulmonary pressure D Measurement of end expiratory lung volume variations EDIC style Type A 12 Disadvantages of
12. Langue Francaise Intensive Care Med 1999 25 1444 1452 PMID 10660857 Full text pdf THINK Conventionally we distinguish between lung damage due to high distending pressure barotrauma and lung damage due to high lung volume volutrauma Think whether this distinction is justified and useful In particular reflect on the following points Respiratory physiology tells us that distending pressure and lung volume are just different expressions of the same phenomenon i e respiratory system distension When we reason in terms of pressure we can evaluate easily and unambiguously the risk of over distension The same evaluation is much more difficult if we reason in terms of volume Maximum acceptable Fr In severe ARDS A low Vt can to some extent be compensated by increasing the compensation Fr However increasing Fr has an important drawback the for the low ey i increasing of Fr expiratory time Te may fall sufficiently to impede complete a exhalation to the equilibrium point defined by the applied Sa de sii Exhalation is PEEP Reaching equilibrium within the end of Te depends on much faster due the balance between Te and the respiratory system expiratory tolow time constant RCe compliance combined with nearly normal RCe corresponds to the product of resistance and compliance resistance and quantifies the speed of exhalation With a Te of at least i three times the RCe the equilibrium is at least nea
13. a PEEP even higher than 15 pulmonary vasoconstriction cmH 0 When a high PEEP level is considered major attention should be paid to monitoring haemodynamics as well as organ perfusion to minimise adverse effects ANECDOTE a 31 year old male with Legionella infection developed ARDS Worsening hypoxia and respiratory distress necessitated emergency intubation and ICU admission The ventilator was set to VCV FiO 100 PEEP 8 Tv 6 5ml Kg IBW plateau pressure 28 cmH20 Static compliance of the respiratory system was 24mL cmH20 po 70 mmHg 9 3 kPa pCO2 44 mmHg 5 8 kPa pH 7 32 The clinicians decided to set PEEP to 12 cmH20 plateau pressure and arterial pressure were unchanged while compliance improved to 29 mL cmH20 Unexpectedly pO2 worsened to 60 mmHg 8 0 kPa The PEEP trial was repeated after a fluid challenge 500 ml colloids with a marked improvement in gas exchange pO 123 mmHg 16 3 kPa pCO 42 mmHg 5 5 kPa pH 7 33 For an extensive review of the pulmonary and extrapulmonary adverse effects of PEEP see also Navalesi P Maggiore SM Positive end expiratory pressure In Tobin MJ editor Principles amp Practice of Mechanical Ventilation 2nd ed New York McGraw Hill 2006 p 273 325 Tidal volume reduction to 6ml Kg and limiting plateau airway pressure to below 30 cmH 0 are widely accepted elements of a lung protective strategy PEEP titration to prevent inter tidal alveolar collapse and to k
14. and adapt the zoom accordingly Virtual MV CurviLin B Collapse EasyTrigger General instructions Word File Virtual MV is a general mechanical ventilation simulator It allows the simulation of volume controlled ventilation VCV pressure controlled ventilation PCV and pressure support ventilation PSV in actively breathing or passive patients CurviLin allows the simulation of alveolar recruitment and over distension CurviLin is based on a curvilinear static pressure volume curve for the respiratory system and shows how a passive VCV breath moves along the curve depending on ventilator settings and patient ventilator interaction B Collapse allows the simulation of a COPD patient with expiratory bronchial collapse and favourable interaction between external PEEP and intrinsic PEEP EasyTrigger is a mechanical ventilation simulator focused on patient initiation of mechanical breaths It allows simulation of pressure trigger and flow trigger with selectable trigger sensitivity 53 Self assessment SELF ASSESSMENT QUESTIONS EDIC style Type K 1 Invasive ventilation includes A All positive pressure ventilation B Ventilation using an endotracheal tube C CPAP using a tracheostomy tube D CPAP using mask ventilation 2 Initiation of a breath cycle Must be started by a patient initiated inspiratory effort Will always be aborted by a patient initiated inspiratory effort Machine initiated breath are star
15. either assisted spontaneous when pressure support is set above zero or fully spontaneous when pressure support is set to zero e Pressure Control SIMV PC SIMV This mode is the same as SIMV except that the mandatory inflations are developed with pressure control rather than of volume control For more information on freestanding CPAP systems see the following reference a es Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 p 177 Fig 7 11 CPAP circuit Cairo JM Pilbeam SP McPherson s respiratory care equipment 8th ed St Louis Mosby International 2008 p 362 363 40 Task 4 General working principles of positive pressure ventilators Dual control modes This category includes several modes designed for combining the advantages of pressure control with those of volume control The dual control of inspiratory pressure and tidal volume is made possible by various sophisticated techniques based on closed loop control applied to mechanical ventilation In recent years the number of different dual control modes offered by mechanical ventilators has overtaken the number of conventional primary modes The use of a variety of names for these modes by ventilator manufacturers further complicates their classification Breath to breath dual control can generate special forms of PCV PSV and PC SIMV in which the inspiratory pressure is automatically adapt
16. endotracheal intubation includes all of the following EXCEPT Loss of the protective function of the upper airway Loss of phonation Decreased airway resistance Damage to the subglottic area Need for sedation and or analgesia ciotoli 13 The figure shows A Volume controlled ventilation B Pressure assisted spontaneous breathing C Volume assisted spontaneous breathing D Bilevel Positive Airway Pressure Ventilation 55 Self assessment E Pressure controlled ventilation Pressure E Volume si Tima 14 Effective methods to decrease an elevated PaCO2 may include all of the following EXCEPT Increase tidal volume Increase frequency Decrease circuit dead space Increase PEEP Increase inspiratory pressure OO WD 15 Adverse effects of PEEP include the following EXCEPT A Over distension of normal alveoli B Barotrauma C Decreased cardiac output D Increased intracranial pressure E Increased cyclic collapse of unstable alveoli 16 To increase oxygenation during IPPV all of the following are useful EXCEPT Increase FiO Increase PEEP Decrease I E ratio Increase peak inspiratory pressure Alveolar recruitment m ga w e 56 Self assessment Self assessment answers Type K A F IAF JAT IAT AF JAT JAF JAF JAF JAT AT Type A 12 Answer C is correct 13 Answer E is correct 14 Answer D is correct 15 Answer E is correct 16 Answer C is correct 57 Win F
17. in restrictive lung disease while in obstructive lung disease it is important to select a low frequency and a low I E ratio The ventilator settings should then be adjusted trying to gently move the patient towards the optimal targets In very severe restrictive lung disease BIPAP ventilation can be useful BIPAP may allow maintenance of spontaneous respiratory activity while supporting oxygenation with high but safe pressure levels prolonged duration of the upper positive pressure phase and even inverse ratio between the upper and lower pressure phases Oxygenation is optimised by finding the most appropriate combination of FiO and the various interventions aimed at achieving alveolar recruitment PEEP normally plays a major role but we must not forget that several aspects of the management of ventilation may favourably affect oxygenation De escalation and weaning Weaning patients De escalation is a process that is started as soon as the OO patient s respiratory state begins to improve and there is really a matter of consensus see Boles JM below that consideration of de ventilation modes escalation and weaning from the time of initiation of and techniques ventilation is useful Rather it is based on good clinical bie i ractice and This and other identified key aspects of weaning a ene ETRO de escalation are well addressed in the consensus publication to a timely de referenced below escalation of the different De
18. mechanical support In all ventilators in which monitoring is not based on proximal sensors high compliance and high resistance also result in poor estimates of the actual values for most of the monitored variables Circuit replacement Before use a ventilator must be equipped with a complete external circuit with filter s The set can be either new single use sterile or clean or re usable Re usable sets must have been cleaned and decontaminated after the previous use Nore Ra assembling and attaching each new circuit a tightness test must be performed For some ventilators manufacturers instructions also prescribe performing other tests and or calibration procedures after attaching a new circuit For information on cleaning and disinfection see the reference below es Cairo JM Pilbeam SP McPherson s respiratory care equipment 8th ed St Louis Mosby International 2008 During long term ventilation the complete circuit with filters is periodically replaced An unequivocal circuit replacement policy has not been established Several prospective randomised trials have demonstrated that the frequency of ventilator circuit change does not affect the incidence of ventilator associated pneumonia VAP Torres A Ewig S Lode H Carlet J European HAP working group Defining treating and preventing hospital acquired pneumonia European perspective Intensive Care Med 2009 35 9 29 Full text pdf An HME if present
19. more information about monitoring of mechanical ventilation read the PACT module on Respiratory monitoring optimal monitoring is achieved when ventilators are equipped with pressure and flow sensors at the airway opening For reliable results the ventilator must have been properly calibrated Integral capnometry is an option provided only by a few ventilators because expired gas monitoring is usually included in the bedside vital signs monitor Modern ventilators for intensive care provide extended monitoring functions including e Graphic monitoring of the important mechanical signals from the Graphic ventilated respiratory system airway pressure flow and volume monitoring presented as real time curves and pressure volume or isa useful flow volume loops function in e Numeric monitoring from automatic breath analysis intensive Care e Alarms and messages regarding patient and ventilator status N Carefully choose the alarms you activate and the alarm limits Too many alarms and too strict limits may result in nearly continuous alarming thus making your patient anxious while the attention of the nurses to the alarms may eventually decrease Some ventilators also provide functions for special measurements of respiratory mechanics such as e Manual end inspiratory hold for assessment of static end inspiratory pressure plateau pressure 48 Task 4 General working principles of positive pressure ventila
20. of those available to date Manual measurements with a double prolonged occlusion manoeuvre at end inspiration and end exhalation will provide further clarification Manual measurements on the static screen with end inspiratory and end expiratory pauses of 4 seconds indicate data as follows see also figure below Ppeak 45 cmH2O Ppause 25 cmHs0 PEEP 8 cmHs0 PEEPtot 13 cmHs0 Vt 520 ml End Insp Flow 0 7 l s 68 Patient Challenges Volume ml 01203456 7 8 9 10 11 12 13 14 seconds LEARNING SSUES Ventilator monitor manual measurements of passive mechanics Q It is possible from the above data to calculate derived indices of respiratory mechanics If you opted to do this what are the values for maximum inspiratory resistance Rmax quasi static compliance Cqs respiratory system time constant RC and intrinsic PEEP PEEP A Rmax 45 25 0 7 28 5 cmH 2O I s Cqs 520 25 13 43 ml cmH20 RC 28 5 x 43 1000 1 23 sec PEEPI 13 8 5cmH20 You repeat the measurements while PEEP is temporarily lowered to zero ZEEP Results are similar to those with PEEP viz the PEEP is 6 cmH O Rmax 31 cmHs0 1 s Cqs 40 ml cmH 0 and RC 1 2 sec After resuming the previous PEEP of 8 cmH 0O with passive VCV Vt 520 ml frequency 18 bpm and FiO 0 6 the arterial blood gases ABGs reveal a pH of 7 23 PaCOz of 67 mmHg 8 8 kPa and PaO of 62 mmHg 8 2 kPa Q How do you interpret
21. or assisted breathing observation of the flow curve provides a qualitative assessment of dynamic hyperinflation but quantification of airway obstruction is very imprecise A The clinical information and measured data strongly suggests acute small airway obstruction which may be further evaluated and quantified by measurement of respiratory mechanics performed during relaxed ventilation There is agreement with your suggestion The patient is sedated paralysed with neuromuscular blocker and ventilated using volume controlled ventilation VCV with constant inspiratory flow frequency 18 bpm Vt 520 ml 8ml kg I E 1 2 inspiratory pause 10 and unchanged PEEP of 8 cmH 0O On the ventilator monitor data generated by automatic breath analysis indicate an inspiratory resistance of 23 cmH 2O 1 s and a quasi static compliance Cqs of 27 ml cmHs0 The end expiratory flow is far from zero An end expiratory occlusion manoeuvre indicates a PEEPtot of 13 cmHo0 This suggests a high level of intrinsic PEEP PEEPi of 5 cmHs0 which optimally requires confirmation of automatic breath analysis data by manual measurements LEARNING ISSUES Ventilator monitor automatic analysis of passive mechanics Q If a fully comprehensive picture were desired why are the above data not sufficient and what might you perform in addition A Data confirm small airway obstruction but PEEPI is the only reliable measurement of respiratory mechanics
22. patient with a low compliance 20 ml cmH20 and a normal expiratory resistance 12 cmH 0 1 s including the circuit is passively ventilated with PEEP of 12 cmH20 Vt of 400 ml and frequency of 22 b min If you increase the I E to 2 1 would you expect significant dynamic hyperinflation and if so why How can you check for this A Significant dynamic hyperinflation is not to be expected with an I E of 2 1 because the expiratory time of 0 9 sec would correspond to more than three times the expected expiratory time constant of 0 24 sec Actual dynamic hyperinflation can be checked by measuring intrinsic PEEP with an end expiratory occlusion manoeuvre Q In the case above knowing that the patient has an IBW of 80 kg how do you assess and judge the safety of the set Vt of 400 ml A With an IBW of 80 kg and a Vt of 400 ml the Vt kg is 5 ml kg However with compliance of 20 ml cmH 0O total PEEP of 12 cmH20 and Vt of 400 ml the theoretical static end inspiratory pressure is rather high 32 cmH20 If a high plateau pressure is confirmed by an end inspiratory hold manoeuvre some further reduction in Vt should be considered Management of oxygenation PaQOz2 target Normoxaemia is the ideal target In an individual patient Normoxaemia however the PaO target should be chosen considering the is usually invasiveness and adverse effects of the treatments aimed at saat da PaQ2 improving oxygenation as well as the general clinical condition
23. physiology for supplementary information Gas exchange between the alveolar spaces and the mixed venous blood flowing through the pulmonary capillaries takes place continuously The alveolar spaces therefore continuously lose Oz and collect CO2 In order to maintain adequate gas exchange the alveoli are flushed with fresh gas rich in O2 and free from COs When the standard control of pH and PaCo conflicts with mechanical Safety criteria normally priority is given to mechanical safety If it is considered that the consequent pCO pH is potentially injurious to the specific patient alternative strategies need consideration This alveolar flush is achieved by the tidal volume Vt delivered at a given respiratory frequency Fr It is intermittently inhaled and exhaled on top of the functional residual capacity FRC the volume of gas remaining in the lung at end expiration However only part of the Vt the alveolar volume VA works as alveolar flush Part of the Vt the dead space volume Vd corresponds to the parts of the respiratory system that are not involved in gas exchange airways and non perfused alveoli Hence only a proportion of the total minute ventilation MV Vt Fr is useful for supporting gas exchange This is the alveolar ventilation V A VA Fr The rate of elimination of CO from the respiratory system is proportional to the V A The control of PaCO and hence the respiratory contro
24. pressure trigger and flow trigger Note how the delay in the ventilator response depends on the ventilator settings for trigger type and sensitivity but also on Level of spontaneous activity Dynamic pulmonary hyperinflation Q What is the main principle for setting the trigger sensitivity whether pressure or flow triggered A Trigger sensitivity should be set at a high sensitivity i e a low number to reduce the ventilator response delay This improves patient ventilator interaction and patient comfort A very high sensitivity can generate ventilator self cycling auto triggering In conventional Inspiration Volume control vs pressure control volume control the constant Conventional volume controlled inspiration is based on square wave control of the instantaneous inspiratory flow delivered for the andthe set inspiratory time and according to the set flow pattern to decelerated achieve the set tidal volume Inspiratory flow pattern are the most 36 common choices Task 4 General working principles of positive pressure ventilators At any instant of a volume controlled inspiration the The inspiratory pressure developed at the airway opening depends on the pressure controlled balance between the by the ventilator above the baseline e Inspiratory flow and volume change produced by the is referred to as ventilator and Control Passive impedance of the respiratory system resistance EE
25. should observe the principle of using the lowest FiO that ensures satisfactory oxygenation An FiO of 0 6 is considered safe even when administered for long periods Higher levels of FiO may be toxic for the lungs but are sometimes used even for long periods when clinically necessary to avoid serious hypoxaemia Note Hypoxic pulmonary vasoconstriction HPV increases pulmonary vascular resistance in poorly aerated regions of the lung thus redirecting pulmonary blood flow to better ventilated regions HPV can be inhibited if the patient is ventilated with high FiO or if alveolar hypoventilated units are recruited local increase in P aO 2 Alveolar recruitment See Charles Gomersall video on shunt Hypoxaemia due to true intrapulmonary shunt is refractory to high FiO In this instance in order to improve hypoxaemia non ventilated lung regions should be re opened i e recruited to ventilation Depending on the aetiology recruitment can be achieved with a range of manoeuvres For instance bronchial suction is effective in atelectasis due to bronchial plugs Drainage of pleural effusions or pneumothorax is effective when atelectasis is due to lung compression Also reduction of increased intra abdominal pressure may have a beneficial effect on alveolar recruitment and oxygenation In inhomogeneous diffusely diseased lung e g ALI ARDS alveoli may be poorly ventilated or collapsed but unstable During mechanical ventil
26. to a reduction in the delivered Vt and should decrease the inspiratory time in favour of expiration Q What other reasons to support the need to decrease the PS level A The elevated level of support lead to tidal volumes greater than 10ml kg which are higher than the limits recommended in acute lung injury patients to prevent ventilator induced lung injury One of your colleagues feels that a high level of support in this patient may help in unloading the respiratory muscle and proposes to increase sedation to decrease the respiratory drive of the patient Q Give some reasons why his choice may not be appropriate A First at high PS levels decreasing the respiratory drive by sedating the patient may have little effect on the delivered Vt that as already discussed above is too high Second preservation of spontaneous activity may have several advantages in terms of gas exchange less need of sedation and faster weaning Using a high pressure support level reduces the patient respiratory work which may lead to atrophy of respiratory muscles and subsequent difficult weaning Third though the patient may not yet be ready for full weaning he appears able to participate actively in minute ventilation without risk of respiratory muscle exhaustion Q You decrease progressively the PS level while checking the patient s own respiratory rate During the trial procedure you obtain the following data PS 15 ventilator RR 22 bpm patie
27. 130 mmHg CO 7 6 L min SvO 77 PEEP 16 Plateau 32 cmH20 Crs 30 mL cmH320 pO 135 mmHg CO 6 5 L min SVOs 72 Q How do you interpret the results A The increase in PEEP produced an improvement in oxygenation and Crs Plateau pressure increased by less than the increase in PEEP suggesting alveolar recruitment However from PEEP 14 to PEEP 16 Crs slightly decreased suggesting possible over distension of ventilated alveoli 64 Patient Challenges Moreover at PEEP 16 CO and SvO decreased Overall PEEP 14 appears to be the best compromise Q Would you attempt another RM A The increase in Crs during the previous RM was higher than the Crs we obtained with the increase in PEEP Now that we have a higher PEEP an RM could have a more sustained effect You perform a second 40 seconds 40 cmH30 sustained recruitment manoeuvre arterial systolic pressure and oxygen saturation do not significantly change during the manoeuvre After 20 minutes ABG improve PaO 170 mmHg 22 4 kPa PaCOz 46 6 1 kPa pH 7 36 Crs increases to 37 ml cmH20 plateau pressure decreases to 27 cmHs0 Intrapulmonary shunt decreases to 23 FiO is progressively reduced to 0 6 to maintain a PaO of more than 75 mmHg 9 9 kPa The patient gradually improves and is de escalated and weaned from mechanical ventilation after seven days A 73 year old lady is admitted to your ICU for treatment of pulmonary thromboembolism PTE after hip repl
28. 4 Lellouche F Mancebo J Jolliet P Roeseler J Schortgen F Dojat M Cabello B Bouadma L Rodriguez P Maggiore S Reynaert M Mersmann S Brochard L A multicenter randomized trial of computer driven protocolized weaning from mechanical ventilation Am J Respir Crit Care Med 2006 15 174 894 900 In some patients complete weaning is impossible most often due to failure to recover from the underlying respiratory disease 11 Task 2 Initiating and de escalating mechanical ventilation In patients receiving mask ventilation de escalation involves periods of full spontaneous breathing with or without CPAP In patients with tracheostomy the last step is normally represented by intermittent ventilation with periods of PSV alternated with periods of spontaneous breathing on CPAP tracheostomy collar or T piece In orally or nasally intubated patients extubation can be performed directly after a period of PSV at a level of 5 to 8 cmH20 and a PEEP level of 2 to 5 cmH O If necessary mechanical support can be continued non invasively after extubation Link to ESICM Flash Conference Miquel Ferrer Barcelona Role of non invasive ventilation in weaning Vienna 2009 Q Shortly after extubation your patient unexpectedly becomes hypoxaemic PaQ2 54 mmHg 7 2 kPa with an FiQ2 of 0 6 and dyspnoeic with hypocapnia alkalaemia and no sign of airway obstruction The patient is conscious and co operative After clinical assessment w
29. 4 Choice of tidal volume and frequency scccsessssssessescccccccceccecscssssssesscecceccesececesssssssesescececessesescs 16 COM WO 1 RAR E E A 18 lacca 19 occ 19 IR 20 Llano 20 LOR lia 26 Assist respiratory m scle lata 26 Matching the inspiratory flow demand of the patient ccssssssssesscscccccccceececssssesessescsccceceees 29 Intrinsic PEEP PEEP and role of PEEP x ccscosnascaanceccseensbacestaeeseusnisieenisenessagaswunsdonssenstsanekasesaweatends 30 4 General working principles of positive pressure ventilators rien 33 licia arno 33 Inspiratory valve expiratory valve and ventilator CIrCuit ieri 39 lc 34 SAI IL Reena ON EEE ate E I ent ert Mable E nT acne OR O TTT 34 VEWEIALOLY CyCle WAS CICA cavccsisentrsaccercievzetan ciation abiaiadeenianganeniav isa 34 baseline pressure PEEP CPAP iatale 34 Phases of the ventilatory iis 35 X enon mO E e E REA 39 Conventional Riel 40 bilia 41 PRICE ii 42 PU ZI AIA ALIVE MOLE AIR RATTI RO E OTO OTT 43 CIO IRA 43 ERANO CI sssrin 44 Active NIDI Oi 44 A E E a E 1 EE I E T AA E AO N A AAAI A AEN NSA AE ET E EEEO PE EA AT 45 Parella aa 45 Circuit dead space compliance and TEM 46 C E LR 0 T ROOT 47 Venlilator maintenant uccisi 47 Ventilator O AR RE O NT OTO 48 BATE o PR OE RR OTO O SOT O O age ent meee eens 52 lucca 53 cina 54 ARR 58 Learning objectives LEARNING OBJECTIVES After studying this module on Mechanica
30. Med 2004 351 4 327 336 PMID 15269312 Meade MO Cook DJ Guyatt GH Slutsky AS Arabi YM Cooper DJ et al Lung Open Ventilation Study Investigators Ventilation strategy using low tidal volumes recruitment maneuvers and high positive end expiratory pressure for acute lung injury and acute respiratory distress syndrome a randomized controlled trial JAMA 2008 299 6 637 645 PMID 18270352 Mercat A Richard JC Vielle B Jaber S Osman D Diehl JL et al Expiratory Pressure Express Study Group Positive end expiratory pressure setting in adults with acute lung injury and acute respiratory distress syndrome a randomized controlled trial JAMA 2008 299 6 646 655 PMID 18270353 Several approaches have been proposed to selecting the most appropriate level of PEEP at the bedside In clinical practice selection of the PEEP level is very complex Gas exchange is the most commonly used guide to the selection of the level of PEEP PEEP should be increased at least to a level that achieves adequate oxygenation with a safe FiOz lt 60 and should consider Besides blood gases the selection of PEEP can also be based on benefits and adverse information about recruitment assessed by measurement of effects both actual lung mechanics measurements and or imaging standard chest and potential X ray and CT scan Link to ESICM Flash Conference Claude Gu rin Lyon PEEP management in critically ill patients Peep titrati
31. Ri max quasi static compliance Cqs respiratory system time constant RC and intrinsic PEEP PEEPi The requirements for valid measurements are e Patient temporarily relaxed with sedation and neuro muscular blocking drugs e Volume controlled ventilation VCV set with a constant inspiratory flow e An end inspiratory hold manoeuvre of 4 seconds e An end expiratory hold manoeuvre of 4 seconds 49 N os E gt a Volume ml Oo 2 23 4 amp 5 6 7 8 9 101112713 14 seconds Task 4 General working principles of positive pressure ventilators In ventilated adults with normal airway resistance Vei Cq RC PEEPi Ri max is usually 5 8 cmH20O 1 s including the effect of an unobstructed endotracheal tube of appropriate size The clinical interpretation of measurements of respiratory system compliance is easier when referred to the ideal body weight normal value 1 1 2 ml cmH20 kg Ppeak peak airway pressure Ppause static end inspiratory pressure PEEP positive end expiratory pressure PEEPtot total intrapulmonary PEEP end inspiratory flow Vt tidal volume Ri max Ppeak Pp ause V ei a SRO Ppause PEEPtot Ri maxeCqs PEEPtot PEEP Frozen curves during passive VCV with constant inspiratory flow and double hold manoeuvre for manual measurement of passive respiratory system mechanics Ppeak Ppause PEEP PEEPtot MEASUREMENT TYPE PATHOPHYSIOLOGICAL MEANING
32. a M Corte FD Navalesi P Physiologic response to varying levels of pressure support and neurally adjusted ventilatory assist in patients with acute respiratory failure Intensive Care Med 2008 34 2010 2018 PMID 18629471 Full text pdf Gas conditioning E en Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 p 161 Humidification The inspiratory gas delivered to the patient must be adequately heated and humidified especially when the upper airway is bypassed by an endotracheal tube or tracheostomy Gas conditioning can be achieved by means of a e Heat and Moisture Exchanger HME mounted at the Y piece or e Heated humidifier mounted within the inspiratory tubing 43 Task 4 General working principles of positive pressure ventilators r ije The Passive humidification SRO _ Hus NE dead space and HMEs are otherwise known as passive humidifiers or artificial resistance of noses HMEs work by collecting heat and humidity from the HMEs depend expired gas on the specific product High HMES produce an increase in apparatus dead space and neat a LS resistance When an antimicrobial filter is coupled to an HME a S ssociated with further increase in dead space and resistance usually results Special small size HMEs are designed for use in infants and children high dead i on HMEs are simple to Advantages of HMEs include low cost and simpl
33. acement She is obese 95 kg with an estimated ideal body weight of 65 kg and there is no previous history of respiratory disease She is receiving i v heparin On the third night due to rapid respiratory deterioration she is intubated and mechanically ventilated The next morning the patient is lightly sedated and being ventilated with pressure support ventilation PSV with an above PEEP pressure support PS level of 15 cmH 0 The PEEP level is set at 8 cmH20O and FiO at 0 6 and humidification is with a Heat and Moisture Exchanger HME She has just become severely dyspnoeic with a respiratory rate of 32 bpm and Vt of 400 ml There is some wheezing on auscultation but otherwise no other evidence of superimposed or complicating pathology LEARNING ISSUES Causes of respiratory failure Assessment of adequacy of ventilatory support Choice of humidification device You hear few pathological sounds some rhonchi and wheezing on auscultation ABGs reveal pH 7 24 PaCOz 62 mmHg 8 1 kPa PaO 60 mmHg 7 9 kPa BE 2 mEq l Haemodynamics are satisfactory with low level cathecholamine support The ventilator monitor shows the curves illustrated below You also note that the end tidal CO pressure of 40 mmHg 5 3 kPa is much lower than the arterial PaCO indicating an increased alveolar dead space 65 Patient Challenges N _ 2 LEARNING SSUES Tuning of mechanical support Nore INR clinical case
34. ated with increased ventilation requirements and mechanical dysfunction resulting in high impedance to ventilation Impedence of the respiratory system is most commonly expressed by the quantifiable elements of respiratory system resistance respiratory system compliance and intrinsic PEEP positive end expiratory pressure Intensivists Role of mechanical ventilation ee ee learning for Mechanical ventilation was initially conceived as symptomatic decades and treatment for pump failure The failing muscular pump is are still assisted or substituted by an external pump Because of learning how to technological limitations in the early days substitution was the reenter only choice Today technological advances allow mechanical ente LES ventilators to be used as sophisticated assistants of the A respiratory pump lung failure lung failure In this context the safe management of mechanical ventilation requires precise information about altered respiratory mechanics in the individual patient in order to tailor a strategy that protects the respiratory system from further damage ventilator associated lung injury VALI and provide an environment that promotes lung healing In the most severe cases with extreme mechanical derangements these objectives can be difficult to achieve You can find information on applied respiratory physiology and acute respiratory failure in the following links and references E eS Cha
35. ation application of PEEP or an intentional transient large increase in transpulmonary pressure recruitment manoeuvre RM or a prolongation of the inspiratory time may all recruit collapsed regions Fink M P Abraham E Vincent J L and Kochanek P M editors Textbook of Critical Care 5th Edn Elsevier Saunders Philadelphia USA 2005 p 499 500 20 Task 3 Underlying physiological principles guiding mechanical ventilation ANECDOTE A young lady with severe ARDS secondary to sepsis developed a left pneumothorax that was successfully drained On day six blood gases and chest X ray showed substantial improvement Ventilation was switched from PCV to PSV and PEEP was decreased from 15 to 12 cmH20 The following day she was tachypnoeic tachycardic and in pain Oxygenation was poor while the chest X ray looked unchanged The left chest tube was still draining a small amount of air during inspiration The level of sedation was increased and PEEP was re escalated to 15 cmH20 but these manoeuvres resulted in worsening of haemodynamics and no improvement in blood gases A CI scan of the chest was then obtained showing an anterior pneumothorax causing extensive compression of the left lung and totally separated from the existing pleural drain A colleague reminded staff that increasing PEEP is not the only treatment for poor oxygenation in ARDS is not always the most appropriate response and that therapy needs to be targeted to the specifica
36. ation in intensive care refer to the PACT module on Acute respiratory failure and the first reference below See the second reference for information about interfaces and ventilators specifically designed for non invasive ventilation a en Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 176 179 Continuous positive airway pressure Branson RD Hess DR Chatburn RL editors Respiratory care equipment 2nd ed Philadelphia Lippincott Williams and Wilkins 2000 p 593 ISBN 0781712009 Strategies and timing se i la es See underlying The basic concept of initiating mechanical ventilation is not physiological difficult and entails setting the inspired oxygen concentration principles in FiO2 and positive end expiratory pressure PEEP to control Task 3 which starts with management of CO2 elimination patient oxygenation and attending to the tidal volume Vt and respiratory rate frequency Fr as controllers of CO2 elimination The choice of the most appropriate ventilation mode and settings may be complex but most centres make regular use of a limited number of modes familiarity with which is fairly straightforward 6 Task 2 Initiating and de escalating mechanical ventilation The successful application of the principles See Tasks 3 and 4 relies on the correct recognition of the clinical context of each patient described by at least fo
37. ation of passive mechanics data You can simulate the ventilation conditions necessary for the measurements activate the hold manoeuvres read the data necessary for calculation and calculate the results by the appropriate equations Check the typical curves and loops associated with obstructive or restrictive lung disease and with intrinsic PEEP After training on Virtual MV try to repeat the same measurements and observations on real patients with the ventilators in your ICU 51 Conclusion CONCLUSION This module has outlined e The nature of respiratory failure e How to approach mechanical ventilation and set up a ventilator incorporating a general strategy for ventilatory support which includes non invasive and invasive approaches e An understanding of the underlying physiological principles including an approach to the nature of the underlying respiratory disease and its evolution the different physiological tasks to be managed and lung protective ventilation e How mechanical ventilators work and how to take full advantage of the information provided by the monitoring system of the ventilator to modify and optimise the ventilator therapy for patient benefit 52 Appendix APPENDIX There are four original computer based interactive tools Excel files with separate worksheets To view the simulators properly graphics and data together it is recommended you use a screen resolution of 1024x768 or higher
38. cling means that the ventilator switches to exhalation as soon as the set inspiratory time Ti has elapsed According to the philosophy of the user interface of the ventilator the Ti can be set by different means i e directly as a time in seconds or indirectly depending on the combination of different settings such as e Duty cycle Ti or the Inspiration Expiration ratio I E combined with frequency e Inspiratory peak flow combined with tidal volume and flow pattern Time cycling is used in controlled and assist control breaths A limitation of time cycling is that the machine is unable to adapt to changes in the spontaneous ventilatory pattern An increase in spontaneous frequency may result in critical shortening of the expiratory time and hence in dynamic pulmonary hyperinflation unless the ventilator Ti setting is manually adjusted to match the patient s own Ti Patient controlled cycling is used in assisted spontaneous and Using ETS fully spontaneous breaths Patient cycling is based on an een da lt expiratory trigger that allows the automatic adaptation of the STRESA Pa Co ventilator Ti to the patient s own Ti The expiratory trigger is spontaneous or based on instantaneous measurement of the inspiratory flow fully When the inspiratory flow falls below a threshold value the spontaneous ventilator considers that the inspiratory effort should be close to breaths while the end and hence cycles to exhalation Depending o
39. cough and fever max 39 C before attending the emergency department for worsening dyspnoea Chest X ray revealed right middle and lower lobe consolidation and bilateral patchy infiltrates In the emergency department the patient had stable haemodynamics slightly tachycardic but peripheral saturation of haemoglobin was poor SpOz 88 and deteriorating despite the use of an oxygen mask with a reservoir bag He was subsequently sedated intubated as an emergency and admitted to the ICU Initial ventilation was with Volume Controlled Ventilation VCV mode FiO 1 PEEP 10 cmH 0 Vt 700 ml and RR 20 Inspiratory peak and mean airway pressures were 40 and 20 cmH 0O respectively Haemodynamically he was stable with HR 100 bpm 61 Patient Challenges BP 110 70 mmHg CVP 9 mmHg ABG PaO 70 mmHg 9 2 kPa PaCOs 40 mmHg 5 3 kPa pH 7 40 Core temperature was 38 C LEARNING SSUES Pump failure and or lung failure Different reasons for hypoxaemia Mechanical ventilation See also the PACT modules on Acute respiratory failure and Respiratory monitoring The patient is sedated to tolerate MV paralysed with repeated boluses of muscle relaxant as needed and breathing 100 oxygen Q Why is the patient so hypoxaemic A Probable reasons for hypoxaemia are shunt due to perfusion of non ventilated lung regions true intrapulmonary shunt One could in this patient also consider a ventilation perfusion mismatch shunt effect b
40. d the limit of effective Vt 4 4 functional residual capacity FRC of the lung Pleural pressure and FRC determination at the bedside are still not very common in clinical practice For further reading see Chiumello D Carlesso E Cadringher P Caironi P Valenza F Polli F Tallarini F Cozzi P Cressoni M Colombo A Marini JJ Gattinoni L Lung stress and strain during mechanical ventilation for acute respiratory distress syndrome Am J Resp Crit Care Med 2008 178 346 355 At the bedside plateau pressure the pressure observed during a relaxed end inspiratory hold can be easily measured A plateau pressure of 25 cmH 0O is always considered safe A pressure of 30 cmH 0 is probably safe in most cases Higher values are not recommended The static end inspiratory pressure depends on a number of factors besides the Vt namely PEEP intrinsic PEEP and compliance This means that a relatively high Vt of 12 15 ml kg is within pressure safety limits when compliance is normal high and total PEEP is low On the contrary a Vt as low as 6 ml kg can produce excessive plateau pressures when the compliance is extremely low and a high PEEP level is applied 16 Task 3 Underlying physiological principles guiding mechanical ventilation International consensus conference in intensive care medicine Ventilator associated lung injury in ARDS American Thoracic Society European Society of Intensive Care Medicine Soci t de R animation
41. due to the difficulty of maintaining PEEP and controlling pressure and volume within safe limits RM can be performed either manually by temporarily changing the ventilator settings or automatically by activating a periodical sigh function RM can significantly improve oxygenation in the short term with few adverse events mainly transient and self limited hypotension and desaturation during the manoeuvre Clinical outcome benefits of delivering RMs are still unclear so this technique is not recommended as standard treatment in mechanically ventilated patients and should be carefully employed only in selected cases It is nevertheless useful to recall that recruitment manoeuvres combined with high PEEP could be considered in early severe ARDS patients with life threatening hypoxemia 25 Task 3 Underlying physiological principles guiding mechanical ventilation Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 231 232 Body position changes Patient position Changes in patient position may improve oxygenation Periods of ventilation in the lateral position with the best lung down are indicated in prevalent one lung injury allowing better ventilation and recruitment of the non dependent lung and improvement in regional ventilation perfusion matching In diffuse lung injury periods of ventilation in the prone position may also lead to significant improvement in oxy
42. during PCV PSV and PC SIMV The optimal assistance of the respiratory muscles involves Appropriate choice of ventilation mode and Fine tuning of ventilator settings A a With Virtual MV Appendix simulate a high spontaneous respiratory activity e g a spontaneous frequency of 30 b min and a peak muscular pressure Pmus max of 20 cmH O With different ventilation modes try to provide a 29 Task 3 Underlying physiological principles guiding mechanical ventilation substantial level of positive pressure above PEEP throughout inspiration and find the best settings to avoid intrinsic PEEP In VCV it may be a challenge Best results are obtained by increasing the peak flow i e by increasing Vt decreasing Ti and using a decelerated flow pattern If your Ti setting is longer than the patient s Ti significant intrinsic PEEP may be generated In PCV it is easier You can adjust only the controls for inspiratory pressure Pinsp and Ti In PSV it is much easier You can adjust only the Pinsp control while the ventilator Ti tends to be automatically matched with the patient s respiratory muscle Ti Intrinsic PEEP PEEPi and role of PEEP In ALI and ARDS if PEEP is successful in achieving alveolar recruitment and improving respiratory system compliance the mechanical ventilatory load decreases as long as PEEP is not so high as to push tidal ventilation into the upper section of the pressure volume relationship wh
43. e minimise intrinsic PEEP In restricted patients with ARDS a reduced only toa higher I E may improve alveolar recruitment and oxygenation limited extent by increasing the mean pressure applied to the respiratory because this increases the system Interestingly in patients with severe restrictive lung een arene ner disease we can even apply a moderately inversed I E like 2 1 ui sia without generation of relevant intrinsic PEEP thanks to the low peak airway RCe with high exhalation speed typical of these patients pressure However inversed I E increases the mean intrathoracic pressure and may compromise the circulation CEA ajustments to the I E ratio should be matched with frequency The choice of both parameters should be guided by the principle that a Te RCe ratio of at least 3 and never lower than 2 should be achieved A bry to apply the concepts outlined above with the interactive tool Virtual MV Appendix Start with passive Volume Controlled Ventilation VCV Check the effects of different levels of minute ventilation and selections for Vt Fr and I E while simulating patients with normal lungs restrictive or obstructive lung disease Find out the effective and the deleterious settings while trying to prevent Excessive peak airway pressure Excessive static end inspiratory pressure Intrinsic PEEP 18 Task 3 Underlying physiological principles guiding mechanical ventilation Q An ARDS
44. eart and risks inducing acute cor pulmonale Bronchial obstruction worsens CO elimination which was already impaired due to the direct effect of PTE LEARNING SSUES Pump failure or lung failure Role of PEEP and intrinsic PEEP on respiratory mechanics and gas exchange You decide to try to optimise the ventilator settings Q What is your PaCOz target and what minute ventilation may be required Justify your answer A Due to PTE significant hyperventilation would be required to achieve a normal PaCOs The patient showed dynamic hyperinflation due to the presence of bronchial obstruction and an insufficient expiratory time Therefore respiratory rate should be decreased and hypercapnia should be accepted In order to avoid excessive hypercapnia a different ventilation mode could be considered LEARNING SSUES Principles guiding mechanical ventilation Management of CO elimination PaCO and pH targets Alveolar ventilation and minute ventilation Q In the present context what are the alternative choices of ventilation mode A A reasonable choice is to continue passive ventilation facilitated by sedation and if necessary neuromuscular blockade with either VCV or PCV As an alternative you could try BIPAP Ventilation modes Timing and strategies Assistance of respiratory muscles 70 Patient Challenges Q What are your targets for the ventilatory pattern A You should aim to increase the expiratory
45. ed breath by breath to achieve a target tidal volume This principle allows a high degree of freedom for patient ventilator interaction within each breath and the simultaneous control of the average tidal volume Automatic adaptation to changing needs of the patient is the most recent technical challenge in the field of mechanical ventilation Q All breath to breath dual control modes automatically de escalate the inspiratory pressure when patients increase their spontaneous inspiratory activity Provide an example of an advantage and a disadvantage of this feature A Automatic de escalation may result in successful automatic weaning or lead to periods of inadequate assistance of respiratory muscles depending on the needs of the individual patient for ventilatory support Adaptive Support Ventilation ASV is a special form of breath to breath dual control ventilation designed for adaptation of the ventilator to the changes in both passive and active respiratory mechanics of the patient ASV guarantees a minimum minute ventilation by working on a dual control PC SIMV basis The ASV design allows a non conventional simplified user interface with settings for minimum minute ventilation and patient s ideal body weight IBW and no user setting for mandatory frequency tidal volume inspiratory time and pressure support All these parameters are automatically adapted on the basis of minimum ventilation setting the pat
46. eedom from mechanical support and removal of the artificial airway Successful weaning depends on a major improvement in lung function and resolution of critical illness although usually it can be successfully performed before recovery is complete Several indices have been proposed as predictors of successful weaning but no index or combination of indices is 100 reliable for predicting either successful or unsuccessful weaning Successful weaning depends on e General and specific care of the patient leading to the resolution of the indications for mechanical ventilation and e A determined approach to de escalation with a continuous effort to reduce the mechanical support as soon and as much as possible The early measurement of weaning predictors and daily protocolized weaning trials may be useful in the management of weaning In particular a protocol that pairs spontaneous awakening with spontaneous breathing trials can improve the outcome of mechanically ventilated patients es Girard TD Kress JP Fuchs BD Thomason JW Schweickert WD Pun BT Taichman DB Dunn JG Pohlman AS Kinniry PA Jackson JC Canonico AE Light RW Shintani AK Thompson JL Gordon SM Hall JB Dittus RS Bernard GR Ely EW Efficacy and safety of a paired sedation and ventilator weaning protocol for mechanically ventilated patients in intensive care Awakening and Breathing Controlled trial a randomised controlled trial Lancet 2008 12 371 9607 126 3
47. eep the lung open throughout the ventilatory cycle is an important aspect of this strategy PEEP titration to this optimal level is still debated and investigated A tidal volume reduction strategy can maintain the static end inspiratory pressure within safe limits but is likely to involve hypercapnia and even further worsening of hypoxaemia Moreover the higher the PEEP level the more likely are both alveolar recruitment and over distension Three large randomised controlled trials ALVEOLI LOV and ExPress studies comparing low and high PEEP in acute lung injury patients have recently been conducted Despite a lack of benefit in terms of hospital mortality in an unselected population higher levels of PEEP may be associated with a lower rate of rescue therapies and lower hospital mortality in the subgroup of severe ARDS patients 22 Task 3 Underlying physiological principles guiding mechanical ventilation Briel M Meade M Mercat A Brower RG Talmor D Walter SD et al Higher vs lower positive end expiratory pressure in patients with acute lung injury and acute respiratory distress syndrome systematic review and meta analysis JAMA 2010 303 865 873 PMID 20197533 Brower RG Lanken PN MacIntyre N Matthay MA Morris A Ancukiewicz M et al National Heart Lung and Blood Institute ARDS Clinical Trials Network Higher versus lower positive end expiratory pressures in patients with the acute respiratory distress syndrome N Engl J
48. enna can control tidal volume during pressure controlled ventilation advantages of by applying closed loop control techniques This kind of pressure management referred to as dual control inspiration control and achieves tidal volume control volume control Either within each breath by automatically switching from pressure control to flow control when the system finds that the set tidal volume cannot be obtained by pure pressure control Or by pure pressure control with automatic breath to breath adjustments of the inspiratory pressure applied by the ventilator 37 Task 4 General working principles of positive pressure ventilators A Ne With the simulator Virtual MV Appendix you can explore the differences between volume control and pressure control by alternating the view between Volume Controlled Ventilation VCV and Pressure Controlled Ventilation PCV Start with the simulation of a passive patient with normal mechanics then simulate bronchial obstruction or pulmonary oedema and finally simulate increasing spontaneous respiratory activity Q What is the inspiratory flow pattern during PCV in a passive patient A During passive PCV the flow pattern is non linearly decelerating The instantaneous flow is not pre set Deceleration is faster when compliance is lower and slower when resistance is higher Cycling to exhalation Machine vs patient When controlled by the machine cycling is normally time based Time cy
49. ent in the dependent and basal lung regions thanks to the tone and pump action of the diaphragm and e Reduces the positive intrathoracic pressure associated with mechanical ventilation thus decreasing the adverse effects of positive pressure on haemodynamics and extrathoracic organs Hence the choice of the ventilation mode and settings should be designed to maintain at least some spontaneous respiratory activity whenever possible while avoiding patient discomfort mechanical stress on the lungs and increased oxygen consumption due to muscular activity In the most severe ARDS cases options are limited sedation is necessary and sometimes muscle relaxants neuromuscular blocking drugs cannot be avoided Q In severe ARDS why might Biphasic Positive Airway Pressure BIPAP be a sensible choice A BIPAP or Bi level allows safe and effective maintenance of spontaneous respiratory activity while exploiting the recruitment effect of an imposed ventilatory pattern with prolonged inspiration and even reversed I E ratio A similar ventilator pattern applied by conventional PCV usually requires patient pharmacological paralysis Recruitment manoeuvres The periodic delivery of passive breaths at high pressure and volume may improve alveolar recruitment and oxygenation Currently there is no consensus about the role safety and best mode for delivering recruitment manoeuvres RM Manual bagging can be dangerous in severe lung injury
50. entilator rapidly drops the During airway pressure to the baseline level which is maintained until exhalation the next breath starts When the next cycle is a controlled the ventilator breath the duration of the expiratory phase depends on the always ventilator settings for frequency and Ti Otherwise the duration works as a depends on the patient For more details on ventilatory cycle Serna management consult es Cairo JM Pilbeam SP McPherson s respiratory care equipment 8th ed St Louis Mosby International 2008 pp 365 387 Ventilation modes The ventilation mode represents a specific operating logic or software program for the mechanical ventilator based on one or more approaches to respiratory cycle management When different forms of management are possible these can be alternative alternated in different periods or even superimposed in the same period A modern classification of ventilation modes should distinguish between Conventional primary modes Dual control modes Biphasic pressure modes Patients effort driven modes 39 Task 4 General working principles of positive pressure ventilators For more on ventilatory support see es Ventilatory support indications In Waldmann C Soni N Rhodes A editors Oxford Desk Reference Critical Care Oxford Oxford University Press 2008 ISBN 13 9780199229581 p 6 Conventional primary modes This category includes all the classic con
51. ere there will be significant over distension and reduction in compliance A Ne With the interactive tools CurviLin Appendix simulate a restrictive lung disease patient with a lower inflection point LIP of 10 cmH 0O an upper inflection point UIP of 30 cmH O and a best compliance Crs of 25 ml cmH20 With a Vt of 460 ml progressively increase PEEP starting from zero and check how tidal ventilation moves along the static pressure volume curve The effective compliance Cqs improves and hence work of breathing decreases then Cqs worsens again when tidal ventilation moves beyond the UIP During assisted ventilation intrinsic PEEP PEEP is an additional source of impedance that opposes both the inspiratory muscles and the ventilator throughout the entire inspiration Any ventilator adjustment that decreases PEEP will improve the effectiveness of mechanical assistance During protective ventilation assessment of intrinsic PEEP is recommended since the reduction in tidal volume may trigger an increase in the respiratory rate which could eventually lead to an increased intrinsic PEEP a en Hough CL Kallet RH Ranieri VM Rubenfeld GD Luce JM Hudson LD Intrinsic positive end expiratory pressure in Acute Respiratory Distress Syndrome ARDS Network subjects Crit Care Med 2005 33 527 32 30 Task 3 Underlying physiological principles guiding mechanical ventilation A Ne With Virtual MV Appendix you can simula
52. escalation involves adjustments to FiO PEEP and components of ventilatory support mechanical support De escalation can be started with any ee ventilation mode and normally it is continued with PSV by patient s condition stepwise reductions in FiO2 PEEP and pressure support improves Depending on the evolution of the underlying disease de escalation may be short hours or take a long time days or even several weeks and may be interrupted by periods of no progress or re escalation when the patient s condition deteriorates Link to ESICM Flash Conference Martin Tobin Maywood Prediction of difficult weaning Vienna 2009 10 Task 2 Initiating and de escalating mechanical ventilation en Boles JM Bion J Connors A Herridge M Marsh B Melot C et al Weaning from mechanical ventilation Eur Respir J 2007 29 1033 1056 PMID 17470624 In patients with severe lung injury or left ventricular failure de escalation of positive pressure and of PEEP in particular should be performed particularly carefully and slowly PEEP de escalation should be based not only on frequent blood gases but also on lung mechanics and imaging confirming a real improvement in lung function When PEEP de escalation is too fast oxygenation may dramatically worsen and recovery may be slow Weaning is sometimes confused with de escalation It is the final step in de escalation involving the patient s complete and lasting fr
53. failure hypercapnia and respiratory acidosis Inadequate alveolar may cause ventilation may result from a number of causes intrinsically lung failure affecting one or more components of the complex pathway that dueto begins accumulation of secretions e Intherespiratory centres pump controller inadequate e Continues with central and peripheral motor nerves ventilation e Ends with the chest wall including both the respiratory and atelectasis muscles and all the passive elements that couple the muscles with the lungs Alveolar hypoventilation may even be seen in the absence of any intrinsic problem of the pump when a high ventilation load overwhelms the reserve capacity of the pump Excessive load can be caused by airway obstruction respiratory system stiffening low compliance or a high ventilation requirement culminating in intrinsic pump dysfunction due to respiratory muscle fatigue 2 Task 1 The nature of respiratory failure Lung failure Lung failure may cause failure Lung failure results from damage to the gas exchanger units ee a alveoli airways and vessels 7 impedance See PACT module on Acute respiratory failure for additional and information increased ventilation Lung failure involves impaired oxygenation and impaired CO Wegener elimination depending on a variable combination of e Ventilation perfusion mismatch e True intrapulmonary shunt e Increased alveolar dead space Lung injury is also associ
54. frequency Management of oxygenation Q Do the ventilator settings need to be adjusted A The patient is ventilated with 10 ml Kg PBW with normal pH and pCO Plateau pressure and tidal volume place the patient at risk for ventilator induced lung injury An attempt should be made to lower tidal volume lt 8 ml kg and plateau pressure whilst tolerating hypercarbia permissive hypercapnia LEARNING SSUES Management of CO elimination You lower the tidal volume to 480 ml by keeping the same PEEP level and increase RR to 26 to prevent an excessive increase in PaCOsz indexed tidal volume is now 6 8 ml Kg PBW plateau pressure is now 30 cmH 0 PEEPi 0 cmH 0 Crs 24 ml cmH20 Mean airway pressure is decreased to 20 cmH20O ABG shows pO 55 mmHg 7 2 kPa pCO 47 mmHg 6 2 kPa pH 7 36 Haemodynamics are HR 95 AP 120 72 mmHg CVP 6 mmHg SvcOsz is low 65 Urine output is 70ml hour Q The new ventilator setting is more protective though the plateau pressure is still high However oxygenation is worse Can you provide some reasons related to the new ventilator setting to explain the decrease in PaOz A By lowering tidal volume we decreased the plateau pressure and mean airway pressure The decrease in mean alveolar pressure may have favoured alveolar derecruitment and worsening of intrapulmonary shunt This possibility is confirmed by the decrease in Crs from 27 to 24 ml cmHx0 LEARNING SSUES Management of severe oxy
55. genation especially in patients with higher potential for recruitment and marked gravitational distribution of lung densities Despite a convincing physiological rationale several recent studies have failed to demonstrate an improvement in overall mortality in acute hypoxemic respiratory failure patients Although it has been suggested that in the group with the worst hypoxemia PaO2 FiOs lt 100 mmHg or 13 5 kPa mortality might be improved prone ventilation is not recommended as standard treatment for ALI ARDS See the following reference for further details es Sud S Friedrich JO Taccone P Polli F Adhikari NKJ Latini R Pesenti A Guerin C Mancebo J Curley MAQ Fernandez R Chan M Beuret P Voggenreiter G Sud M Tognoni G Gattinoni L Prone ventilation reduces mortality in patients with acute respiratory failure and severe hypoxemia systematic review and meta analysis Intensive Care Med 2010 36 585 599 Full text pdf Extrapulmonary shunt When impaired oxygenation is caused entirely by extrapulmonary shunt mechanical ventilation and high FiO An intracardiac will not have any direct benefit on oxygenation Benefits may right to left only arise indirectly for instance due to a reduction in oxygen shunt should be consumption and favourable changes in haemodynamics In the suspected presence of an intracardiac right to left shunt particular whenever a caution should be exercised when applying positive pressure eee
56. genation impairment Alveolar recruitment Recruitment manoeuvres See also module on Acute respiratory failure Though a PaO of 55 mmHg 7 2 kPa could be clinically acceptable in the absence of acidosis or haemodynamic instability it would be preferable to decrease the FiOz which is still set at 1 Q What could you do with the ventilator to improve oxygenation A You could try to promote alveolar recruitment by increasing the PEEP level and or using recruitment manoeuvres Some of your colleagues are reluctant to increase PEEP given the already high plateau pressure Thus in order to improve oxygenation you perform a 40 seconds 40cmHs0 pressure sustained recruitment manoeuvre RM During the manoeuvre arterial 63 Patient Challenges systolic pressure and oxygen saturation drop to 70 mmHg and 80 respectively Five minutes after the end of the manoeuvre Crs increases to 35 ml cmH 0 and PaO increases to 80 mmHg 10 5 kPa You decide to leave the ventilator settings unchanged However after 20 minutes SatO PaO and Crs return to the same values as before the RM Q How do you interpret the effect of RM A The increase in Crs and PaOsz indicate that some alveolar recruitment may have taken place after RM However this effect was short lived suggesting the need of a higher PEEP level to better counteract alveolar derecruitment The important decrease in arterial pressure and oxygen saturation during the RM suggests
57. he application of PEEP can also over distend other lung regions promoting barotrauma with formation of bullae pneumothorax and pneumomediastinum and biotrauma diffuse lung injury and possible injury to other organs due to release of inflammatory mediators Intrathoracic pressure variation due to positive pressure ventilation can also affect cardiovascular function and the distribution of perfusion See Charles Gomersall video on heart lung interaction 21 Task 3 Underlying physiological principles guiding mechanical ventilation Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 171 172 IPPV with PEEP Fink M P Abraham E Vincent J L and Kochanek P M editors Textbook of Critical Care 5th Edn Elsevier Saunders Philadelphia USA 2005 p 499 501 A PEEP level of up to 5 cmHs0 has minimal adverse effects and Severe lung can be used in most patients In the majority of ALI ARDS injury may not cases a PEEP of 10 15 cmH20 is required Brain injury with result in severe raised intracranial pressure is the most important relative NTU MAAN th contraindication to this level of PEEP Attention should be paid ot ne iui to blood volume haemodynamics sodium water retention and cia urine output Tidal volume should be reduced in order to their capacity to prevent ventilator associated lung injury VALI autoregulate hypoxic Very severe ARDS may require
58. he use of accessory inspiratory muscles while attempting to achieve an almost normal level of PaCO It seems reasonable to conclude that the level of pressure support was decreased too rapidly 58 Patient Challenges Q Is the interaction between patient and ventilator satisfactory A Yes in spite of the high respiratory rate there is no dysynchrony between patient and ventilator From the flow and pressure waveform it appears that all the patient s inspiratory efforts are supported by the ventilator Q What can you do to relieve the patient s distress A You could simply increase the pressure support level LEARNING SSUES Assessment of patient ventilator synchrony Assessment of patient respiratory work load You decided to increase the pressure support level to 18 RR respiratory rate decreases to 24 bpm Vt increase to 450 ml while ABGs remain unchanged Po 1 is now 2 cmH 0 The following morning the nurse shows you the following ABGs pH 7 37 PaCOs 45 mmHg 5 9 kPa and PaO 95 mmHg 12 5 kPa The ventilator monitor reports a respiratory rate of 17 bpm with tidal volume between 650 and 750 ml Po 1 is 5 cmHs0 The ventilator monitor provides the curves shown below Pressure cmH 0 a TV ml Flow ml sec a Time sec Though the patient is said not to be uncomfortable you feel the ventilator settings are not optimum Q Given the respiratory rate RR and Vt on the ventilator what ca
59. hich finds no new pathology what might be your first choice of intervention A In a conscious patient with refractory hypoxaemia and no difficulty in maintaining alveolar ventilation CPAP by face mask or helmet should be tried first New modes of The strategy proposed above is based on several ventilation ventilation like BIPAP modes most of which are conventional However single _ and ASV can be used for ventilation modes available today are designed for the entire theentiremanagement management of complex respiratory failure cases from of respiratory failurein initiation to complete weaning Examples of such modes intubated patients from include initiation of support to weaning e Biphasic Positive Airway Pressure BIPAP This very open approach to the setting of ventilation parameters allows in expert hands safe and effective use in a variety of clinical conditions The main limits of this mode are the total lack of volumetric control and the general concept being more difficult to understand than for most of the other modes e Advanced breath to breath dual control modes with the capability of automatically switching between full ventilatory support and partial ventilatory support see Task 2 12 Task 3 Underlying physiological principles guiding mechanical ventilation 3 UNDERLYING PHYSIOLOGICAL PRINCIPLES GUIDING MECHANICAL VENTILATION Mechanical ventilators can be used to e Control CO e
60. ient s theoretical deadspace and monitored variables as well as lung protective and best energetics criteria Different models of ventilators have different modes of dual control ventilation You should consult the user s manual of your ventilator and see the following reference for information on dual control modes and ASV Iotti G ed Closed loop control mechanical ventilation Respir Care Clin N Am 2001 7 3 397 408 and 425 440 41 Task 4 General working principles of positive pressure ventilators Biphasic pressure modes In these modes the ventilator controls only pressure which moves between a lower and an upper level at a given user set frequency and duty cycle If the patient is making spontaneous respiratory efforts these are freely superimposed on the variable pressure level independently from the phase of the ventilator cycle Depending on the range of frequency of the change from high to low pressure the biphasic pressure modes can be classified as different forms of Biphasic Positive Airway Pressure BIPAP and different forms of High Frequency Ventilation HFV ae With BIPAP the ventilator applies a dual CPAP level with a esters lower and an upper PEEP set by the user The periodical time eer cycling between the two CPAP levels is one source of alveolar the BiPAP ventilation The second source of alveolar ventilation is based ventilator an on the spontaneous breaths superimposed by the patien
61. ifferences in time pene constants of different ventilatory units The major difference e Increased I E ratio between external PEEP and intrinsic PEEP is technical the e Spontaneous former is entirely controlled by the ventilator while the latter respiratory activity depends on the dynamic balance between ventilator and e Recruitment patient Intrinsic PEEP can be easily measured in passively ina Patient positioning ventilated patients but continuous monitoring is difficult Therefore improving recruitment by artificially generating intrinsic PEEP cannot be considered a safe practice In ARDS when oxygenation is severely impaired a sensible approach includes the setting of an I E ratio higher than normal but not so high as to generate intrinsic PEEP Inverse ratio ventilation IRV i e ventilation with an I E ratio 24 Task 3 Underlying physiological principles guiding mechanical ventilation greater than 1 1 requires deep sedation and sometimes even patient pharmacological paralysis unless the Biphasic Positive Airway Pressure BIPAP mode is used and periodical verification of the level of intrinsic PEEP Maintenance of spontaneous respiratory activity a en Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 174 176 Spontaneous modes of respiratory support Spontaneous respiratory activity e Improves ventilation distribution and recruitm
62. ificially bypasses the upper airway to the The invasiveness lower third of the trachea with a reliable pneumatic seal Such of endotracheal tubes have a number of advantages RO IS s e Protecting the lungs from major aspiration SI SoA shies l i or maximum e Protect the upper airway and gastrointestinal tract from safety and positive pressure flexibility e Relieving upper airway obstruction e Providing easy access to the airway for suction and bronchoscopy e Reducing dead space e Enabling a stable and safe connection between the ventilator apparatus and the patient If necessary tracheal intubation enables ventilation modes that provide full control of ventilation The invasive approach to mechanical ventilation has however a number of disadvantages associated with tracheal intubation including e Loss of the protective functions of the upper airway heating and humidification of inspired gases and protection from infection e Decreased effectiveness of cough risk of sputum retention atelectatsis e Increased airway resistance e Risk of airway injury e Loss of the ability to speak These disadvantages do not apply to non invasive mechanical ventilation NIMV In carefully selected patients see below NIMV is more comfortable and reduces the duration of mechanical ventilation and the incidence of ventilator associated pneumonia VAP For further information about tracheal intubation read the following reference 4 Task
63. ified sii a management of humidification and the ventilator circuit N When tidal volume and minute ventilation are very high When there are major air leaks In severe hypothermia When secretions are blood stained or particularly thick The performance of HMEs can be inadequate HMEs are not indicated When secretions are very abundant due to risk of clogging the filter and need for frequent changes In patients with severe impairment in CO elimination because of additional dead space When tidal volumes need to be limited as in patients with ARDS Acute Respiratory Distress Syndrome Q Why do major air leaks contraindicate the use of HMEs A With major air leaks the volumes exhaled by the patient through the HME are much lower than the inspiratory volumes delivered by the ventilator Therefore the heat and moisture collected by the HME are insufficient for adequate gas conditioning Nore M is advisable to choose an HME with low dead space and low resistance especially for unsupported spontaneous breathing Active humidification Heated humidifiers can vary in their level of sophistication Advanced humidifiers are provided with an automatic filling system inspiratory tube warming with a heated wire temperature control at the Y piece smart algorithms for humidity control and alarms Active humidification 44 Task 4 General working principles of positive pressure ventilators e D
64. ile the patient is dyspnoeic and appears to be fighting the ventilator The ventilator screen shows the curves below Paw cmH Disadvantage of machine cycling in actively breathing patients Cycling to exhalation Machine vs patient Q What is wrong and how would you intervene A The patient has started spontaneous breathing at high frequency The fixed inspiratory time of PCV now generates inverse I E resulting in a major increase in intrathoracic pressures due to dynamic hyperinflation You should either Disconnect the patient from ventilator and take control with careful manual ventilation Thoroughly review the ventilator settings for instance by reducing the inspiratory time or switching to PSV while re adjusting the inspiratory pressure level Or Re administer neuromuscular blockade to paralyse the patient Q Has anything been forgotten in the treatment Prompt Do not forget to combine aetiological treatments when available A Bronchodilators The airway obstruction has not been treated but just compensated by appropriate settings of the ventilator 74 Patient Challenges The treatment is continued with sedation paralysis and passive ventilation with low frequency low I E ratio and low PEEP A agonist is added and the dose of i v heparin is increased On the following day sedation is reduced and a trial with PSV is successful De escalation of mechanical support is continued slow
65. imary modes of ventilation Sedation is frequently necessary but total suppression of spontaneous respiratory activity and pharmacological paralysis should be avoided whenever possible Modes with pressure controlled management of inspiration PCV PC SIMV BIPAP PSV allow a better matching between the patient s flow demand and ventilator flow delivery when compared to modes such as VCV and SIMV The inspiratory pressure should be set to achieve a balanced spontaneous respiratory activity neither too high nor too low 9 Task 2 Initiating and de escalating mechanical ventilation Q A patient is assisted by a pressure support level of 10 cmH20 Frequency is 28 b min blood gases and haemodynamics are satisfactory How can you decide whether the spontaneous respiratory load is excessive or not A In addition to observing the respiratory rate and the tidal volume being achieved asking the patient s opinion and observing respiratory coordination are important additional elements for deciding the adequacy of mechanical assistance Although in actively breathing patients the ventilatory pattern is mainly patient controlled the ventilator can powerfully affect the output of the respiratory centre Therefore exactly as in pharmacologically paralysed patients you should formulate optimal ventilatory targets adapted to the type of lung disease e g restrictive or obstructive Again a reduced Vt target should be considered
66. ine expiratory line Y piece and catheter mount for patient connection In practice however the external circuit can vary considerably depending on the location of the expiratory valve and on the system used for gas conditioning Normally the expiratory valve is located inside the machine and the expiratory line serves as a return circuit from the Y piece to the ventilator Several small size ventilators use a single tube circuit with the expiratory valve located close to the patient usually included into a modified Y piece The proximal expiratory valve can be either a non rebreathing system not directly controlled by the ventilator or a valve pneumatically driven by the ventilator In the latter case a small bore tube must be used for connecting the valve to the ventilator When an active humidifier is used the circuit requires water traps for collecting condensate or heated wires in the tubes to avoid condensation Temperature probes are also necessary for monitoring the temperature of gas in the airways and for driving the temperature regulator of the advanced humidifiers 45 Task 4 General working principles of positive pressure ventilators 1 Support arm 2 Inspiratory port with filter 3 Active humidifier 4 Inspiratory line with watertrap 5 Y piece 6 Expiratory line with watertrap 7 Expiratory port 8 Flexible connector 9 Proximal flow pressure sensor 10 Nebuliser A mechanical ventilator for intens
67. iods of low Vt and apnoea What may be the problem A Excessively high levels of pressure support can generate a periodic breathing pattern by lowering the PaCO and suppressing the respiratory drive Targets are selected on the basis of fundamental principles Excessive respiratory distress and fatigue should always be avoided but significant spontaneous activity should be maintained Total suppression of spontaneous activity should usually be avoided However a recent study in severe ARDS a short period of pharmacological muscle paralysis combined fully controlled ventilation was shown to reduce mortality Papazian reference below This general strategy must be adapted to the patient s clinical state by moving more or less towards full spontaneous breathing according to the phase of ventilation management de escalation or escalation respectively Maintenance of some degree of patient spontaneous activity may result in recruitment of dependent lung regions prevention of respiratory muscle atrophy reduction in the demand for sedative drugs and improvement in haemodynamics Similarly an increase in oxygen consumption and a reduction in alveolar pressures are to be expected en Papazian L Forel JM Gacouin A Penot Ragon C Perrin G Loundou A et al ACURASYS Study Investigators Neuromuscular blockers in early acute respiratory distress syndrome N Engl J Med 2010 363 12 1107 1116 PMID 20843245 Link to ESICM F
68. ion can take place during assist control assisted spontaneous and spontaneous breathing modes O How can machine initiation and patient initiation coexist in assist control breaths A In assist control breaths when the patient s respiratory rate overcomes the frequency set in the machine breaths are patient initiated i e assisted Should the patient stop breathing the machine takes over by delivering controlled breaths according to the set frequency With pressure trigger the ventilator monitors the airway Flow triggering i is always pressure during the expiratory phase When the patient i EEA contracts their inspiratory muscles the airway opening pressure an expiratory drops below the baseline When this drop reaches a pressure base flow in the threshold defined by the trigger sensitivity control the machine ventilator responds by initiating the inspiratory phase of the respiratory circuit The cycle base flow allows the l patient to With flow trigger the ventilator senses the gas flow When the generate the patient contracts their inspiratory muscles the airflow reverses initial from end expiratory or zero to inspiratory When the inspiratory flow inspiratory flow generated by the patient reaches the trigger and reachthe sensitivity threshold the machine responds by initiating flow trigger inspiration threshold a with the interactive tool EasyTrigger Appendix you can explore the differences between
69. it may be necessary to either e Maintain strict control of ventilation by using volume controlled Sound principles for management of mechanical ventilation include Appropriate choice between non invasive and invasive ventilation Maintenance of spontaneous respiratory activity if possible Adaptation of the ventilatory pattern to the nature of lung disease restrictive or obstructive Optimisation of alveolar recruitment Lung protective strategy ventilation VCV pressure controlled ventilation PCV biphasic positive airway pressure BIPAP or synchronised intermittent mandatory ventilation SIMV or PC SIMV SIMV using pressure control to determine the Vt set with relatively high mandatory frequency see Task 4 for detail of these ventilator modes Or if possible e Allow a greater degree of patient ventilator interaction by using pressure support ventilation PSV BIPAP or alternatively SIMV PC SIMV at low mandatory frequency Even in the most severe cases VCV is not always a necessary choice in the 7 Task 2 Initiating and de escalating mechanical ventilation modern context PCV may be a more sensible choice for lung protection In very severe lung disease either restrictive or obstructive the choice of ventilator settings can be more important than the choice between VCV and PCV The ventilatory pattern should be selected according to the type of lung disease Low fre
70. ith a dangerously high static pateo H2O at end inspiratory pressure plateau pressure i e An increase in Vt and or Fr anda decrease in I E ratio can be airway pressure associated with a dangerous increase in peak airway pressure Avoiding intrinsic e An increase in Fr and or I E can be associated with an undesirable PEEP intrinsic PEEP In turn static end inspiratory pressure peak airway pressure and intrinsic PEEP depend on respiratory system passive mechanics namely compliance resistance and time constants i e the product of resistance and compliance DEFINE PACO AND PH TARGETS Choose Minute Ventilation and ventilatory pattern NO Mechanical safety respected YES PaCQO gt and pH targets achieved ves gt eT a NO Permissive approach RE DEFINE PACO AND PH TARGETS Aggressive approach Basic algorithm for setting mechanical ventilation to control PaCO and pH while maintaining mechanical safety In adults a reasonable starting point is an MV setting of 100 ml kg min related to the ideal body weight IBW of the patient However the MV necessary for good control of PaCOz and pH is often much higher due to high CO production and impaired lung function and you will have to choose between e An aggressive approach to be followed as long as the ventilator settings do not conflict with mechanical safety criteria 15 Task 3 Underlying physiological principles guiding mechanical venti
71. ive care with the external circuit Photo GALILEO ventilator Hamilton Medical Switzerland Additional parts of the circuit may include e Antibacterial filter at the inspiratory port of the ventilator e Antibacterial filter at the expiratory port of the ventilator necessary only on a few ventilators e Nebuliser in the inspiratory line e Sensors or sensor ports for pressure flow and expired gas COs analysis Circuit dead space compliance and resistance The mechanical features ofthe The size of the circuit must be proportional to the patient s size circuit can be The inner diameter of the tubes should be optimised by removing any unnecessary e 22 mm for adults rire e 15 mm for children and infants well as choosing e 10 mm for neonates an appropriate length and size When choosing an external circuit you should consider of the tubes especially for i the common e Artificial dead space depends on the volume of all the airway between elements interposed between the Y piece and the patient the Y piece and e Circuit compliance depends on the total circuit volume and Patient elasticity of tubes e Circuit resistance depends on the geometry of the tubes and sufi resistance of added elements 46 Task 4 General working principles of positive pressure ventilators High dead space compliance and resistance of the circuit are all independent elements that decrease the effectiveness of
72. l care and Environmental hazards Infection inflammation and Sepsis Kidney Injury and Metabolism Abdomen and nutrition Peri operative ICM surgery and imaging Education and Ethics Education and assessment Consultant to the PACT Board Dermot Phelan Francesca Rubulotta Anders Larsson Jan Poelaert Marco Maggiorini Mauro Oddo Carl Waldmann Janice Zimmerman Johan Groeneveld Charles Hinds Torsten Schroder Gavin Lavery Lia Fluit Graham Ramsay Copyright 2011 European Society of Intensive Care Medicine All rights reserved Contents Contents a a PROPRIE 1 t Te at re Of reprae I naa S 2 Panpi areor Me E RIA 9 2 RE RR E NER N E S 2 P E e RE IE 05 3 Role of mechanical Velo g 2 Initiating and de escalating mechanical Ventilation ssssssessesescececcccceececscssssessescsceccceseeeeeeees 4 Invasive VS Non invasive eil 4 ll gui 6 Miane I 0 skis Meck 10 010 CIERRRPRRPRRSTO SO RESOR RR 7 Escalation and MIAIN EN ANC isiss aiioisciecivicednscasesvceesu conden dented shnsetuvestannseseusabeiwaksonsoonerenhecsadsesearsassanenaauresion 7 Peli ai 10 3 Underlying physiological principles guiding mechanical ventilation 13 Management of CO elimination alveolar ventilation sssssssssssscscccccccceecessssessssessccccecceeeeeasees 13 Ola Raiano 13 Alveolar ventilation and minute ventilation ovcesdcccnucecessawzanaxrinvenccessansonsensenwacveawssbwencwaspnsuanenvecasuucntess 1
73. l of pH depends on the balance between the V A and the metabolic production of CO V COsz PaCO k V CO VA During mechanical ventilation we manipulate the V A to achieve predefined targets for PaCO and pH Since in clinical practice we do not know the factor k that expresses how difficult the CO elimination is or the V CO of our patients the manipulation of V A is necessarily made by repeated attempts checking the results of any change in settings in terms of PaCO and knowing that an increase in V A will result in a decrease in PaCO and vice versa The matter is made more complicated by the fact that we do not directly control the V A Rather we control minute volume MV and the way the MV is delivered i e the ventilatory pattern defined by Vt Fr and I E ratio 14 Task 3 Underlying physiological principles guiding mechanical ventilation Note It is important to appreciate for example that reducing apparatus dead space by e g changing from a Heat and Moisture Exchanger HME to an active humidifier will increase V A for the same MV On the one hand the possible choices of ventilatory pattern AEE al affect the relationship between MV and V A at constant MV inne beer teers V A decreases when Fr increases volume at 6ml Kg IBW On the other hand the choices are limited by mechanical safety Limited static end criteria inspiratory pressure max e An increase in Vt can be associated w
74. l ventilation you should i Understand the mechanical causes of respiratory failure 2 Have the knowledge to institute mechanical ventilation safely 3 Understand the principles that guide mechanical ventilation 4 Be able to apply these principles in clinical practice FACULTY DISCLOSURES The authors of this module have not reported any associated disclosures DURATION 9 hours Introduction INTRODUCTION The mechanical ventilator is an artificial external organ which was conceived originally to replace and later to assist the inspiratory muscles The primary function of mechanical ventilators is to promote alveolar ventilation and CO elimination but they are often also used for correcting impaired oxygenation which may be a difficult task The concept and implementation of ventilation is relatively straightforward in most patients and clinicians starting to work in Intensive Care usually become familiar with the everyday workings of initiating maintaining and de escalating weaning patients from mechanical ventilation using the modes of ventilation commonly used in that particular environment This module deals with the everyday facets of such care but also addresses in some detail the approach to difficult ventilation problems in patients with severe complex and evolving lung disease Although the mechanical ventilators can be lifesaving they may at the same time be hazardous machines In depth knowledge of mechanical
75. lash Conference Laurent Papazian Marseille Acurasys neuromuscular blocking agents early in the course of severe ARDS Vienna 2009 An excessive level of support may also lead to an increase in patient ventilator dysynchrony mainly due to ineffective triggering ea Thille AW Cabello B Galia F Lyazidi A Brochard L Reduction of patient ventilator asynchrony by reducing tidal volume during pressure support ventilation Intensive Care Med 2008 34 1477 86 Full text pdf 28 Task 3 Underlying physiological principles guiding mechanical ventilation a with Virtual MV Appendix increase the spontaneous activity of the patient by increasing the Pmus and observe the different results during VCV and PSV PO 1 occlusion pressure at 0 1 sec negative pressure generated by the inspiratory muscles in the first 100 msec of an inspiratory attempt with airway occlusion i e in the absence of flow and intrathoracic volume changes PO 1 of 1 5 cmH20 are expected in healthy subject at rest while it may increase to 5 cmH20 during exercise Values of PO 1 are affected by the level of sedation presence of PEEPi and respiratory muscles atrophy The assessment of the results is normally based on clinical examination and monitored variables Ventilatory variables such as Vt Fr and Fr Vt are most commonly used Variables expressing more specifically the degree of muscular activity of the patient like Po 1 can be of great help f
76. lation eOr a permissive approach involving less ambitious blood gas targets and in particular accepting a degree of hypercapnia Choice of tidal volume and frequency A given minute ventilation MV can be delivered in several possible combinations of Vt and Fr However in an individual patient several of the possible combinations may not be very effective or may even be hazardous In patients with severe lung disease selection of the most appropriate Vt and Fr is critical and should be based on effectiveness and safety Minimum effective Vt When Vt is decreased to a value close to the Vd then V A and CO elimination become close to zero even in the presence of high Fr and maintained MV If we consider that the in series Vd anatomical Vd is approximately 2 2 ml per kg of IBW it is not advisable during conventional convective ventilation to apply a Vt of less than 4 4 ml kg i e double the minimum Vd in adult patients In ARDS a Vt of 6 Maximum safe Vt ml kg IBW is strongly recommended The maximum Vt that can be safely delivered is much more However in the most difficult to predict maximal stress tension developed by lung sai eee pepe a tissue fibres in response to pressure and strain tissue be too high and the deformation due to volume can be determined by measuring best choice may transpulmonary pressure i e airway pressure minus pleural approach the minimum pressure AP1 distending the respiratory system an
77. limination e Improve impaired oxygenation e Assist rest the respiratory muscles Mechanical ventilation can be hazardous however as it may have injurious consequences for lung parenchyma and extrapulmonary organs Accordingly significant efforts of the critical care scientific community have been expended to find a lung ventilation strategy to minimise ventilator associated lung injury VALI Note ee may be caused by delivering excessive airway pressures barotrauma or volume volutrauma moreover the repetitive opening and closing of lung regions during tidal ventilation may cause shear stresses atelectrauma eventually cellular inflammatory response may develop biotrauma At the present time there is wide consensus that tidal volume restriction to 6ml Kg IBW ideal body weight and or plateau airway pressures limited below 30cmHs0 may prevent lung injury Discussion still exists about the optimal management of positive end expiratory pressure level and respiratory system recruitment Plateau airway pressure is measured at end inspiration in static conditions of the respiratory system It may be obtained by performing an end inspiratory measurement while the patient is sedated and a neuromuscular blocking drug has been administered Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 163 166 Respiratory changes and ventilator associated lung injury
78. lly identified clinical problem PEEP PEEP is defined as an elevation of transpulmonary pressures at In ALI ARDS and the end of expiration PEEP contributes to the re opening of cardiogenic collapsed alveoli and opposes alveolar collapse thus improving ere abit V Q matching PEEP increases the functional residual capacity ine EE n FRC and by increasing the number of alveoli that are open to applying a PEEP ventilation improves lung compliance and oxygenation The application of PEEP is limited by extrapulmonary and o Se pulmonary adverse effects Ventilation with PEEP increases the se SE transmural pressure applied to the alveoli which may right ventricular contribute to re opening and stabilising of collapsed alveoli The filling thus decreasing application of PEEP can be lung protective since it prevents cardiac output and atelectrauma caused by cyclic collapse and re opening of worsening unstable alveoli oxygenation When testing PEEP effects it For information on the open lung theory see these references ri arene SES volume status of the patient Lachmann B Open up the lung and keep the lung open Intensive Care Med 1992 18 6 319 321 PMID 1469157 Rouby JJ Lu Q Goldstein I Selecting the right level of positive end expiratory pressure in patients with acute respiratory distress syndrome Am J Respir Crit Care Med 2002 165 8 1182 1186 No abstract available PMID 11956065 Unfortunately t
79. low mlsec Pressure omtt 0 Patient Challenges PATIENT CHALLENGES A 64 year old man was admitted to the ICU for severe community acquired pneumonia He has a normal weight 65 kg with a history of smoking one pack a day for more than 30 years but no previous pulmonary disease was reported On admission to the ICU he was intubated and mechanically ventilated After four days he was receiving pressure support ventilation In view of the clinical improvement sedation was reduced and the level of pressure support was decreased to 6 cmH 0O After a few hours you find the patient tachypnoeic respiratory rate 30 35 bpm with a tidal volume between 300 350 ml PEEP of 8 cmH20 and FiO of 0 5 LEARNING ISSUES Causes of respiratory failure Assessment of adequacy of ventilatory support De escalation of ventilatory support See also the PACT module on Respiratory monitoring You hear on auscultation a few inspiratory crackles and bronchial breathing over the consolidated areas Accessory inspiratory muscles were clearly being used ABGs reveal pH 7 38 PaCO 42 mmHg 5 5 kPa PaO 89 mmHg 11 7 kPa You measure an average Po 1 of 7 cmH50 The ventilator monitor provides the curves shown below a OE O daN 250 500 7 50 Time sec Q How do you interpret the respiratory state of this patient A The patient has had to dramatically increase his respiratory effort which is evident by the elevated Po 1 and t
80. ly with PSV and the patient is successfully extubated after 12 days of ventilation On reflection In the first patient clinical examination coupled with observation of the respiratory waveform trace demonstrated lack of synchrony between the patient and the ventilator and how ventilator adjustments allowed synchrony and improved patient respiratory comfort to be achieved allowing controlled de escalation of ventilation The second case of type 1 respiratory failure illustrated the value of a recruitment manoeuvre and optimising the PEEP level to recruit airways and increase functional residual capacity thus minimising intrapulmonary shunt effect and improving oxygenation Case three was a complex scenario where a combination of pathologies pertained causing a delicate balance between severe intrapulmonary and extrapulmonary shunt and bronchial small airway obstruction The key approaches to finding a favourable ventilation strategy were to Diagnose the underlying diseases Review the ABGs and chest X ray Undertake waveform and data analysis with the patient sedated and relaxed Analyse serial data including respiratory mechanics and haemodynamics Break down the problems and consider the management of the different physiological tasks Identify optimal targets e Monitor the results of your modified ventilator settings and verify their effect benefit This approach though complex and only fully required in a minority of patien
81. n di si controlled and compliance and intrinsic PEEP of the lungs and the patient s i chest wall breaths Pressure Support in During pressure controlled inspiration the ventilator assisted applies a positive pressure above the baseline pressure This spontaneous pressure is theoretically a square wave The ventilator generates breaths and a rapid increase in pressure to the user set level and then iii maintains that pressure throughout inspiration a At any instant of a pressure controlled inspiration the inspiratory flow and volume depend on the balance between the e Inspiratory pressure applied by the ventilator and e Passive impedance of the respiratory system and the patient s muscular activity Although we can set volume control and pressure control to deliver exactly the same tidal volume the effects of these two approaches are very different when the patient s respiratory mechanics or respiratory muscle activity change e Only volume control can guarantee a minimum set level of minute ventilation e Only pressure control can guarantee that the pressure applied by the ventilator will be limited to the pre set value e Only pressure control can guarantee a good matching between the flow delivered by the ventilator and the flow demanded by the patient Dual control inspiration Inspiration cannot be managed by simultaneous instantaneous control of volume and pressure However modern ventilators
82. n the the patient ventilator the threshold Expiratory Trigger Sensitivity ETS nona pori can be either an absolute flow value or a given percentage of ari a enea the peak inspiratory flow usually 25 In most cases the ETS is fixed at a ventilator specific value depending ventilator design In a few ventilators a control is available for setting ETS If we change the sensitivity for instance by increasing ETS to 50 or decreasing ETS to 5 we can respectively advance or delay cycling to exhalation 38 Task 4 General working principles of positive pressure ventilators with Virtual MV you can explore the differences between machine cycling and patient cycling Simulate a patient actively breathing at a frequency of 30 b min and then alternate the view between PCV set with frequency 16 b min and Ti 33 and Pressure Support Ventilation PSV Q Consider a patient with a large increase in spontaneous breathing rate for instance due to sepsis Intrinsic PEEP will probably result with PCV machine cycling but is less likely with PSV patient cycling Why A With machine cycling the Ti is pre set and hence an increase in the patient s frequency results in significant shortening of the expiratory time With patient cycling the I E ratio is automatically adapted to the patient s own respiratory cycle and hence the shortening in expiratory time is less marked Exhalation When cycling to exhalation the v
83. n you say about the measured Po 1 A Po 1 of 5 cmH 0O is unexpectedly high and suggests that the patient has a high respiratory drive On the other hand the RR and Vt on the ventilator seem to indicate a well supported patient 59 Patient Challenges Q How do you interpret the patient ventilator interaction A There are frequent respiratory efforts that fail to trigger the ventilator see pointer arrows on pressure trace above The flow and pressure waveforms show that the patient respiratory rate is higher than the ventilator respiratory rate There is clearly poor patient ventilator synchrony It can be speculated that dynamic hyperinflation was present at the time of attempted triggering This problem is commonly reported when the level of assistance is too high leading to large tidal volumes and long insufflation times in patients with chronic obstructive pulmonary disease Q What can you do to improve patient ventilator synchrony A We interpret the high Po 1 as a sign of patient discomfort due to poor synchronisation between patient and ventilator Thus in spite of the Po 1 we decide to decrease the PS level A possible alternative in some ventilators is to change the cycling off criteria for triggering from inspiration to expiration By decreasing the percentage of inspiratory peak flow at which the ventilator terminates the inspiration from 25 to 40 for example you can anticipate expiration This action may lead
84. nt RR 32 bpm Vt 600 9 2 ml kg MV 13 2 L min Po 1 3 cmH20 PS 12 ventilator RR 26 bpm patient RR 27 bpm Vt 460 7 1 ml kg MV 11 9 L min Po 1 2 cmHo0 60 Patient Challenges PS 8 ventilator RR 32 bpm patient RR 32 bpm Vt 420 6 5 ml kg MV 13 5 L min Po 1 3 5 cmH20 Which level of PS do you think is the most appropriate A A PS level between 8 and 12 seems sufficient to provide adequate support while ensuring that Vt is within the protective range From PS 18 to 12 Po 1 progressively decreases while patient ventilator synchrony improves as indicated by the RR of the ventilator approximating that of the patient Though a RR of 32 may be easily tolerated in a patient well adapted to the ventilator at PS 8 the MV and Po 1 are slightly higher than at PS 12 For these reasons PS 12 may be preferable Q How will you proceed in the forthcoming days A You should progressively decrease the level of PS Consider that introduction of a protocol that includes daily spontaneous awakening trials reduction or suspension of sedatives and daily spontaneous breathing trials may improve the outcome of mechanically ventilated patients in intensive care units Your colleague on the night shift admitted a 51 year old man with severe hypoxia due to suspected community acquired pneumonia from the emergency department He has a body mass index of 30 70Kg PBW The patient had a three day history of shortness of breath dyspnoea
85. oes not increase the apparatus dead space e Does not affect the apparatus expiratory resistance and minimally affects the apparatus inspiratory resistance e Increases the compressible volume of the ventilator circuit Special small size humidifying chambers are designed for use in children and infants Nore NA performance of a good active humidifier is superior to that of the best passive humidifier Unlike any HME a good active humidifier can deliver a water saturated gas with a temperature of 37 C at the patient s upper airway Although HME s are widely used heated humidifiers are advisable at least for the most problematic patients The optimal targets for setting an active humidifier have not The assessment been clearly established Full saturation with water vapour at a of the A i effectiveness of temperature of 37 C at the airway opening seems a sensible nisi approach Only the gas temperature and not the levels of ee ere humidity can be easily monitored and controlled For observations additional information on gas conditioning consult Branson RD Hess DR Chatburn RL editors Respiratory care equipment 2nd ed Philadelphia Lippincott Williams and Wilkins 2000 p 101 ISBN 0781712009 External circuit The external circuit is made of flexible tubes and rigid parts Parts of the external circuit The basic design of the external circuit as represented below in the figure consists of the inspiratory l
86. on the pathophysiologic rational Berlin 2007 Link to ESICM Flash Conference Laurent Brochard Creteil PEEP management in critically ill patients High versus low peep strategies in ALI Berlin 2007 Studying the respiratory system static pressure volume relationship at the bedside can provide useful information to guide the setting of both PEEP and tidal volume In ALI ARDS the quasi static P V curve frequently exhibits a lower and an upper inflection point According to the most recent interpretation the P V curve corresponds to a curve of recruitment that increases progressively in the lower inflection section continues steadily in the intermediate linear section and decreases in the upper inflection section where over distension becomes prevalent Since PEEP acts mostly during expiration by preventing alveolar collapse it is suggested that the expiratory part of the P V curve may be more informative in terms of PEEP setting Accordingly PEEP is titrated by a 23 Task 3 Underlying physiological principles guiding mechanical ventilation decremental PEEP approach The static end inspiratory pressure should not exceed the upper inflection point UIP or 30 cmH 0 whichever is lower except during recruitment manoeuvres The shape of the Other approaches involve analysis of the inspiratory pressure inspiratory time curve shape stress index measurement of the respiratory pressure time system static compliance va
87. onal residual capacity PEEPi intrinsic PEEP PEEPtot total PEEP A Ne Check the effects of favourable interaction between PEEP and intrinsic PEEP by the interactive tool B Collapse Appendix 31 Task 3 Underlying physiological principles guiding mechanical ventilation i ntrinsic PEEP is offset by external PEEP only in patients with expiratory small airway bronchial collapse In other cases of pulmonary hyperinflation such as severe acute asthma or dynamic hyperinflation primarily due to shortened expiratory times external PEEP and intrinsic PEEP have largely additive effects and hence you should be cautious in the use of external PEEP a with Virtual MV Appendix you can simulate the presence of intrinsic dynamic hyperinflation by increasing the respiratory rate and therefore reducing the expiratory time Such increased total PEEP imposed PEEP plus intrinsic PEEP may be minimised by reducing the imposed PEEP level 32 Task 4 General working principles of positive pressure ventilators 4 GENERAL WORKING PRINCIPLES OF POSITIVE PRESSURE VENTILATORS Mechanical ventilators are comprised of four main elements e An internal source of pressurised gas including a blender for air and oxygen e An inspiratory valve expiratory valve and ventilator circuit e A control system including control panel monitoring and alarms e A system for ventilator patient synchronisation For details about the technology of ventila
88. or objectively titrating the external mechanical support As long as adequate alveolar ventilation is maintained and oxygenation is acceptable blood gases are much less important than mechanical or clinical variables for making decisions about the level of mechanical required Note In disorders of respiratory control sepsis and severe hypoxaemia the physiological response to external mechanical support can be diminished or even lost In these cases unless depressant drugs are used the control of excessive spontaneous respiratory activity is difficult and the isolated increases in mechanical support usually just result in unnecessary hyperventilation Matching the inspiratory flow demand of the patient In order to effectively unload the inspiratory muscles the flow demand of the patient must be satisfied during the entire inspiratory period Since the instantaneous flow demand is difficult to predict and variable it is more difficult to guarantee effective ventilation with modes based on a pre set instantaneous flow such as during VCV and the mandatory breaths of SIMV Choosing a mode such as PCV PSV and PC SIMV is preferable because the instantaneous inspiratory flow is not limited and only the inspiratory pressure above PEEP has to be set i e the energy applied by the ventilator to support spontaneous respiratory efforts Modern mechanical ventilators may also allow the slope of the inspiratory pressure waveform to be adjusted
89. ory valve opens while the expiratory valve is closed thus generating an increase in the positive pressure applied to the airway opening and delivering gas to the respiratory system 33 Task 4 General working principles of positive pressure ventilators Ventilator operating valves for inspiration and exhalation During expiration the inspiratory valve closes while the expiratory valve opens thus allowing passive exhalation driven by the elastic recoil of the respiratory system The degree of opening of both valves is accurately and instantaneously controlled by the control system to modulate the pressure and flow delivered during inspiration as well as any positive pressure maintained during exhalation Control system This controls the internal source of pressurised gas including the blender and of the two main valves inspiratory and expiratory The control system works on the basis of the user settings entered by means of the control panel and on the information continuously provided by sensors for pressure and gas flow The control system also provides information to the user by means of the monitoring system and alarms Synchronisation Intensive care ventilators are equipped with technology designed to detect both the start and end of the patient s inspiratory efforts and to synchronise the ventilator inspiratory phase with the patient s inspiratory effort The synchronisation system is based on sensors for airway
90. pressure and flow positioned in the ventilator circuit according to the technical choices of ventilator manufacturers and resulting in an e Inspiratory trigger pressure based or flow based to initiate the ventilator inspiratory phase and e Expiratory trigger to stop the inspiratory phase and cycle to the expiratory phase Ventilatory cycle management Baseline pressure PEEP CPAP During exhalation until a new inspiratory cycle is started the DI ventilator controls a baseline pressure which can be set at zero ro qe or at positive levels commonly called positive end expiratory pressure zero pressure Continuous Positive Airway Pressure PEEP CPAP or positive at In this mode PEEP works on the respiratory system to the airway artificially increase the functional residual capacity FRC opening 34 Task 4 General working principles of positive pressure ventilators See Charles Gomersall video on applied respiratory physiology for information on FRC In modern intensive care ventilators PEEP is achieved by Further appropriate and instantaneous control of the degree of opening Pressure of the expiratory valve In several machines a base flow of gas PPlied on top i o of the baseline runs through the ventilator circuit during the expiratory phase promotes of the cycle compensating for minor leaks and contributing to inspiration effective control of PEEP while the return to the ba
91. provides an opportunity for diagnostic and therapeutic exercises in a complex case of respiratory failure It is not to be used as a guide to mechanical ventilation in PTE No specific ventilatory approach is recommended for PTE Q How do you interpret the respiratory state of this patient A A new embolic episode probably took place The patient presents with a combination of a high ventilation requirement due to high alveolar dead space typical of PTE and increased impedance possibly due to airway obstruction as far as you can judge from the expiratory flow curve and the presence of wheezing The combined action of 15 cmHs0 PS and important inspiratory effort evident from deep drop of Paw with trigger is not sufficient to generate the high ventilation needed to achieve a normal PaCOs and pH Pump failure or lung failure Breath initiation Machine vs patient Ventilator monitor Link to PACT module Respiratory monitoring Q What would help you to gain a better picture of the patient s respiratory state Prompt When a ventilated patient is breathing with difficulty first rule out any technical problem A You need to Check for possible obstruction of ET tube or HME and other technical problems Maximise any possible pharmacological intervention to reverse bronchospasm 66 Patient Challenges Check for appropriate setting of trigger sensitivity whether pressure or flow triggered Obtain a chest X
92. quency and low I E ratio are necessary in severe airway obstruction while low tidal volumes relatively high frequency and increased I E ratios should be selected in severe hypoxaemic restrictive disease In very severe lung disease controlled hypoventilation and permissive hypercapnia should be considered when otherwise not contraindicated In patients with refractory hypoxia supplemental strategies including recruitment manoeuvres increasing PEEP level haemodynamic stabilisation inhaled nitric oxide proning prone positioning and extracorporeal membrane oxygenation should be considered 8 Task 2 Initiating and de escalating mechanical ventilation A possible strategy for the clinical management of mechanical ventilation Respiratory Failure PSV by mask si intubation VCV PCV PSV by mask m ECM maintain possibly avoid recruitment substantial i Et worsening Pures z Spontaneous HA ofspontaneois seems increasing PEEP ii respiratory activity breathing haemodynamic mm stabilisation ri PSV WOW iNO proning PCV PCV low frequency SIMW SIMV PC SIMV PC SIMV BIPAP BIPAP ECMO Il improvement improvement c_ improvement intermittent PSV by mask pa k I tu alli ILL p of we intermittent PSV CPAP by j extubation alternated with CPAP T piece mask helmet Full spontaneous breathing For simplicity the flowchart considers only the conventional pr
93. ray Consider assessment measurements of respiratory mechanics focusing on PEEPI LEARNING SSUES Ventilator monitor Q An HME humidifier is being used Explain why this choice of humidifier may be inappropriate A HMEs increase the apparatus dead space and hence are contraindicated in patients with intrinsic difficulties in CO elimination You replace the HME with a hot water humidifier Q Does this patient need any change in trigger setting A Increasing the sensitivity of the trigger may reduce the inspiratory work of breathing Note It is possible that this patient has a high level of intrinsic PEEP PEEPi and in order to counteract the PEEPI she needs to achieve a considerable increase in her inspiratory effort to trigger the ventilator Increasing trigger sensitivity will not be adequate in such a situation to reduce the excessive inspiratory workload LEARNING SSUES Gas conditioning Circuit dead space compliance and resistance On chest X ray you rule out ET tube obstruction or malposition and you note a small quantity of thick mucus on suction A colleague performs an end expiratory occlusion manoeuvre and measures a total PEEP PEEPtot of 16 cmH 0 much higher than the applied PEEP of 8 cmH20 PEEP is 8 cmH20 LEARNING SSUES Assessment of passive respiratory mechanics see Ventilator monitor 67 Patient Challenges Q How do you proceed with the assessment Prompt During spontaneous
94. riations and measurement of end curve linear expiratory lung volume variations EELV curvilinear or concave can Link to ESICM Flash Conference Hermann Wrigge Bonn provide PEEP management in critically ill patients Pulmonary imaging normato and peep titration Berlin 2007 ApoU ung recruitment A recently published clinical trial introduced the concept of using oesophageal pressure measurement to estimate the transpulmonary pressure as a guide to PEEP selection in ALI ARDS patients Despite no difference in outcome between the conventional and the oesophageal pressure guided groups patients in the latter group had better oxygenation and respiratory system compliance Though promising further studies are needed to confirm clinical outcome benefits E en Talmor D Sarge T Malhotra A O Donnell CR Ritz R Lisbon A et al Mechanical ventilation guided by esophageal pressure in acute lung injury N Engl J Med 2008 359 20 2095 2104 PMID 19001507 Increased I E ratio Increased I E ratio can improve recruitment and oxygenation by two mechanisms e Increased mean airway pressure and e Generating intrinsic PEEP when the expiratory time is critically shortened Both the beneficial and adverse effects of this ventilator generated intrinsic PEEP are similar to those of externally Additional steps to applied PEEP although the distribution of intrinsic PEEP may saad ip the RIN pena be less homogenous depending on d
95. rles Gomersall videos on applied respiratory physiology and acute respiratory failure Hinds CJ Watson JD Intensive Care A Concise Textbook 3rd edition Saunders Ltd 2008 ISBN 978 0 7020259 6 9 pp 195 199 Causes of Respiratory failure Fink MP Abraham E Vincent J L Kochanek PM editors Textbook of Critical Care 5t edition Elsevier Saunders Philadelphia PA 2005 p 571 734 See also the PACT modules on Acute respiratory failure COPD and asthma 3 Task 2 Initiating and de escalating mechanical ventilation 2 INITIATING AND DE ESCALATING MECHANICAL VENTILATION In critical care the indicaton for mechanical ventilation may be simply for the management of ventilatory pump failure e g post operatively or for drug intoxication Often however it is required for acute respiratory failure due to parenchymal lung disease See the PACT module on Acute respiratory failure Invasive vs non invasive techniques In intensive care positive pressure ventilators devices that promote alveolar ventilation by applying positive pressures at the airway opening are most often used To transmit positive pressure to the respiratory system the ventilator must be connected to the patient by means of an interface that guarantees a reasonably effective pneumatic seal Two kinds of interface are used e Tracheal tube or tracheostomy the traditional invasive approach e Mask The non invasive approach Tracheal intubation art
96. rly reached Inthe patient A Te shorter than twice the RCe generates significant dynamic With airway i ages obstruction Fr hyperinflation and intrinsic PEEP accumulates above the Ti externally applied PEEP Fortunately most of the patients low in order to requiring a low Vt have a low RCe due to reduced compliance allow a long Te and hence can be safely compensated by increasing Fr to avoid Conversely in asthma COPD patients for whom a low Fr is dynamic indicated to oppose dynamic hyperinflation the effect of pulmonary hyperinflation airways obstruction can be compensated by a relatively high Vt given that lung compliance is often normal or high 17 Task 3 Underlying physiological principles guiding mechanical ventilation i pe 4 4 ml kg IBW Minimum Vt In series anatomical Vd Maximum Vt Static end inspiratory lt 25 cmH O is safe pressure plateau pressure gt 30 cmH 0 is potentially hazardous Static Vt indexed for IBW lt 8 ml Kg may be safe it may need to be lower depending on the measured indices of barotrauma above gt 8 ml Kg may be hazardous Maximum Te RCe If gt 3 PEEP is absent or Fr irrelevant If lt 2 relevant PEEPI is generated Choice of I E ratio The normal I E ratio is between 1 2 and 1 1 5 corresponding to lesi an inspiratory cycle of 33 40 In obstructed patients a lower patient thel E I E ratio contributes with low Fr to prolong the Te and hence ratio can b
97. seline allows Phases of the ventilatory cycle passive exhalation Mechanical ventilation breaths can be considered as e Controlled e Assist controlled e Assisted spontaneous e Fully spontaneous breaths according to the settings selected for e Breath initiation e Inspiration e Cycling to exhalation BREATH TYPE BREATH INITIATION INSPIRATION CYCLING TO EXHALATION Controlled Machine Flow volume control Machine Frequency setting or pressure control nspiratory time setting Assist control Patient Flow volume control Machine Inspiratory trigger or pressure control Inspiratory time setting Machine Frequency setting Assisted Patient Pressure control Patient spontaneous Inspiratory trigger Pressure support Expiratory trigger setting Spontaneous Patient Pressure control Patient Inspiratory trigger PEEP CPAPsetting Expiratory trigger Classification of mechanical ventilation breaths Breath initiation Machine vs patient Machine initiation means that the breath is initiated at a pre set time according to the setting for respiratory frequency Machine initiation can take place only in the modes that include a control for frequency i e in controlled and assist control breaths see below 35 Task 4 General working principles of positive pressure ventilators Patient initiation means that the breath is initiated by the patient s inspiratory effort by means of a pressure or flow based trigger Patient initiat
98. some haemodynamic impairment it seems reasonable to suspect an acute reduction in venous return due to the increased intrathoracic pressure LEARNING ISSUES Management of severe oxygenation impairment Haemodynamic monitoring Pulmonary artery catheter PEEP See also the PACT module on Haemodynamic monitoring Now you decide to perform a PEEP trial However you are worried about haemodynamic side effects Echocardiography suggests the patient needs some fluid resuscitation and a pulmonary artery catheter is inserted in the left jugular vein to monitor continuously the cardiac output CO and mixed venous oxygen saturation SvOz shows CO 5L min pulmonary artery pressure PAP 28 15 mmHg pulmonary artery occlusion pressure PAOP 13 mmHg SvO 60 Fluid challenge with 10ml Kg crystalloids is then performed CO 7 7L min PAP 27 15 PAOP 12 SvO 3 75 Intrapulmonary shunt is obtained by standard calculations Qshunt Qtotal CcOz CaOz CeO2 CvOz 47 where CcOz is calculated pulmonary capillary oxygen content and CaO and CvO are arterial and mixed venous oxygen content respectively Then you perform a PEEP trial You set PEEP 12 14 and 16 cmH O for 20 minutes You check plateau pressure Crs ABG cardiac output and SvO at the end of each step You obtain the following results PEEP 12 Plateau 29 cmH 0O Crs 28 mL cmH20 pO 80 mmHg CO 7 8 L min SvO2 76 PEEP 14 Plateau 29 cmH30 Crs 32 mL cmH30 pO
99. t driven modes This category includes new modes of assisted spontaneous ventilation in which the level of pressure above PEEP generated by the ventilator is proportional to the patient s respiratory effort P piratory During PAV and NAVA Proportional Assist Ventilation PAV In this mode the er NE by ventilator generates pressure in proportion to patient generated proportional to patient s flow and volume The operator sets the percentage of flow demand If patient s assisted and volume assisted ventilation This ventilation mode demand increases then requires the measurement of respiratory system compliance ventilator assistance and resistance increases proportionally likewise if patient s demand decreases then Neurally Adjusted Ventilatory Assist NAVA This mode MPT ree reer uses the diaphragmatic electrical activity during spontaneous deee inspirations to trigger and control the delivery of ventilator assistance The diaphragm electrical activity is recorded by a multiple array oesophageal electrode positioned in the lower oesophagus The pressure applied to the airway by the ventilator is moment by moment proportional to the diaphragm electrical activity according to a proportionality factor set by the operator Fink MP Abraham E Vincent JL Kochanek PM editors Textbook of Critical Care 5t edition Elsevier Saunders Philadelphia PA 2005 p 505 Colombo D Cammarota G Bergamaschi V De Luci
100. t it includes the effect of tracheal tube resistance but the safety of the observed inspiratory pause pressure is questionable Moreover although FiO has been increased oxygenation has unexpectedly and critically worsened with the new settings Q How do you re adjust the ventilator settings Prompt Always remember that static pressures like the inspiratory pause pressure depend on volumes A In order to decrease the inspiratory plateau pressure you should decrease your target for Vt You cannot compensate for the consequent decrease in ventilation by increasing the frequency otherwise dynamic hyperinflation would worsen once 72 Patient Challenges again compromising the effective reduction in pressures Therefore you must accept a higher PaCO Note FAR choice of Vt depends on the balance between baseline pressure PEEP the requirement for adequate alveolar ventilation and potential damage due to the application of excessive pressures You reduce the Vt to 520 ml by lowering Pcontr to 12 cmH 0 PEEPtot is 9 4 cmH20 with a PEEPI of only 1 4 cmHs0 Ppeak is 25 cmHs0 with an inspiratory plateau pressure of 22 cmHs0 Minute ventilation is 6 8 1 min ABGs reveal pH of 7 24 PaCO of 63 mmHg 8 3 kPa and PaO of 60 mmHg 7 9 kPa Paw femH 0 Volume ml O 12 3 45 amp 7 8 9 10171 12 13 14 15 16 17 18 19 20 seconds The new ventilatory pattern with low frequency low I E and Vt just sligh
101. t on the apparatus biphasic cycle whenever s he wants Contrary to any other primarily ventilation mode the patient is allowed to exhale even during designed for non invasive pressure support ventilation the high pressure phase delivered by the ventilator i e during the pseudo inspiratory phase of the biphasic cycle Typical BIPAP settings provide a relatively low ventilator frequency while the patient breathes at a higher rate on top of both the lower and upper CPAP level Variants of BIPAP also include e Pressure support for assistance of the spontaneous breaths and e Patient synchronisation capability for cycling between the two CPAP levels Airway Pressure Release Ventilation APRV is similar in concept to BIPAP with particular settings The patient is maintained at a fairly high CPAP level that is intermittently released to a much lower CPAP level for a short period of time The intermittent release and resumption of the upper CPAP level generates alveolar ventilation that augments the ventilation provided by spontaneous breathing It aims at improving oxygenation without allowing excess hypercarbia The reference gives information about BIPAP and APRV E en Kuhlen R Guttmann J Rossaint R editors New forms of assisted spontaneous breathing Munich Jena Germany Urban amp Fischer 2001 p 35 65 ISBN 3926762535 42 Task 4 General working principles of positive pressure ventilators Patient effor
102. te a COPD patient with Crs of 80 ml cmH 0 Rrs of 25 cmH 0 1 s a spontaneous frequency of 25 b min and a Pmus max of 15 cmH O If you start PCV with a frequency of 15 b min Pinsp of 20 cmH 0 and Ti of 30 a significant intrinsic PEEP is generated Try to decrease the Ti and check how with the same patient inspiratory effort and ventilator Pinsp ventilation becomes more effective PEEPi decreases while Vt consequently increases as long as the ventilator Ti is not too short In ventilated COPD patients with expiratory bronchial collapse PEEPi is a common finding As represented in the schematic drawing below in this context moderate levels of external PEEP increase the functional residual capacity FRC but at the same time achieve the interesting result of reducing PEEPi and the dynamically trapped volume V tr As a result up to a point total PEEP and the end expiratory lung volume V ee do not increase Therefore during assisted ventilation of COPD patients careful adjustment of PEEP can effectively decrease the ventilatory load Link to ESICM Flash Conference Jordi Mancebo Barcelona PEEP management in critically ill patients Peep selection in COPD Berlin 2007 External PEEP A COPD patient with dynamic hyperinflation and air trapping due to bronchial collapse Effects of external PEEP on ventilation pressures and lung volumes Vt tidal volume V ee end expiratory lung volume V tr trapped volume FRC functi
103. ted on a time cycled basis Itis not possible to mix machine initiated and patient initiated breaths ell 3 Usual ways to detect patient initiated inspiratory efforts include A Bya pressure drop in the ventilator circuit B By a sudden increase in airway resistance C By an inspiratory flow detected in the ventilator circuit D Bya decrease in airway compliance 4 In volume controlled ventilation A Tidal volume is given according to a pre set volume target B If the inspiratory time is fixed the peak and mean airway pressure is independent of pulmonary compliance C Ifthe minute volume and frequency is set it is not possible to adjust the tidal volume D If tidal volume and minute volume is set the ventilator frequency must be set between 10 and 20 breaths per minute 5 Which is are correct statements regarding the inspiratory time Ti A Atthe end inspiratory time the expiration phase always starts B If Tiis set by the Inspiration Expiration ratio the Ti is independent of ventilator frequency C If Tiis directly set the expiratory time decreases with increasing ventilator frequency D Normal Ti is in the range of 3 4 seconds 6 In biphasic positive airway pressure BIPAP A The ventilator generates a dual CPAP level with an upper and lower pressure set by the user B Patients may freely generate spontaneous breaths in the low pressure phase only C Patients are allowed to exhale even during the high pressure phase
104. these values of quasi static compliance Prompt Compliance data cannot be interpreted without considering the patient s ideal body weight and body shape that is considering chest wall compliance A The specific Cqs referred to the ideal body weight is 0 66 and 0 62 ml cmHs0 kg respectively at PEEP and ZEEP These values are not much lower than a normal specific Cqs of 1 ml cmHs0 kg We must consider that the chest X ray shows clear lungs in a small size rib cage surrounded by much fat and heavy breast tissue The slight reduction in total compliance probably depends on the patient s body shape Lung elasticity is probably close to normal 69 Patient Challenges Q A visiting consultant arrives on the ward How would you summarise the information derived from the respiratory dynamics A PTE has been complicated by bronchial obstruction with a clinical picture similar to asthma airway resistance is high PEEPi is relevant even at normal respiratory frequency compliance is just slightly decreased and the expiratory flow curve denotes slow exhalation and confirms dynamic hyperinflation Externally applied PEEP has mainly an additive effect on PEEP in this patient The reduced PaO is mainly due to ventilation perfusion mismatch and not to shunt indicating that externally applied PEEP has minimal effect on improving oxygenation Moreover it increases the intra alveolar pressure further impeding the outflow from the right h
105. time in order to decrease dynamic hyperinflation and PEEPI An expiratory time of at least three times the RC is needed i e of 3 6 seconds Assuming you set an inspiratory time of 1 sec the total cycle time results in 4 6 sec The set frequency should not be higher than 60 4 6 13 bpm The resulting I E will be low equal to 1 3 6 Assuming a minute ventilation of 10 l min Vt would be equal to 770 ml LEARNING SSUES Choice of tidal volume and frequency Choice of I E ratio Q The lungs are clear Mechanically the present PEEP level of 8 cmH50 does not seem to provide relevant benefits in terms of respiratory mechanics What is the cause of the PEEPI A PEEPi does not decrease from ZEEP to PEEP 8 cmH20 suggesting that PEEPI is mainly due to dynamic hyperinflation rather than to flow limitation Therefore you consider a reduction in PEEP especially given the current mode of ventilation is passive However oxygenation is greatly impaired and might worsen further at lower PEEP Q Normally a reduction in PEEP would be expected to be associated with a deterioration in oxygenation Are there possible mechanisms whereby it might be associated with an improvement in oxygenation in this patient A A PEEP reduction might reduce the right ventricular afterload and improve right and left heart function and thus by improving mixed venous POs result in benefit to the arterial PaOs Q What do you do to improve oxygenation
106. tly higher than the ideal 6ml kg combines acceptable inspiratory pressures with near complete avoidance of dynamic hyperinflation Ventilation is just slightly higher than normal while the PaCOsz level is acceptable You consider partial correction of pH by slow bicarbonate administration and decide to wait EN Permissive hypercapnia is not necessarily synonymous with low Vt and absolute hypoventilation Haemodynamics are stable but oxygenation is still considerably impaired A transoesophageal echocardiograph is suggested It shows a patent foramen ovale with right to left shunt especially evident during inspiration EN a pulmonary shunt is the most common cause of hypoxaemia but not the only cause Q How can you try to reduce the extrapulmonary shunt by adjusting the mechanical ventilator A You should try a substantial reduction of PEEP in order to possibly reduce right heart afterload and intracardiac right to left shunt 73 Patient Challenges LEARNING ISSUES Extrapulmonary shunt Paradoxical effect of PEEP on oxygenation You make a trial with PEEP set at zero With unchanged settings for frequency and I E an unchanged Vt of 520 ml is obtained by setting a Pcontr of 12 cmH20 that corresponds to an inspiratory pause pressure of 12 cmHs0 PEEPIi is 2 cmH20 PaO increases to 108 mmHg 14 2 kPa while PaCOz decreases to 58 mmHg 7 6 kPa An hour later oxygen saturation on the SpO monitor suddenly drops wh
107. tors e Manual end expiratory hold for assessment of intrinsic PEEP and occlusion pressure at 0 1 sec PO 1 e Slow inflation manoeuvre for recording the static pressure volume curve of the respiratory system Several of the monitoring functions listed above allow the ventilator to be used as a powerful tool for bedside investigation of respiratory system mechanics e Passive mechanics resistance compliance time constant intrinsic PEEP e Indices of patient spontaneous activity e g PO 1 e Spirometric measurements Volumes times frequencies Modern Data concerning resistance compliance time constants and mechanical intrinsic PEEP provide a full picture of passive lung mechanics ventilators are This is extremely helpful for the safe and effective setting of the ROL aut ventilator and allows you to tailor the ventilatory support to the sce Raa mechanical properties of your patient Unfortunately passive Bano mechanics data provided by automatic breath analysis are not respiratory always reliable especially when intrinsic PEEP is present and function the measurements are not based on special algorithms such as the least square fitting procedure In several instances manual analysis of the curves is necessary Integrated graphic monitoring with capability to analyse on frozen curves together with the hold functions enables easy access to the most important measurements related to passive mechanics Maximum inspiratory resistance
108. tory equipment consult a es Cairo JM Pilbeam SP McPherson s respiratory care equipment 6th ed St Louis Mosby International 1999 ISBN 0815121482 Branson RD Hess DR Chatburn RL editors Respiratory care equipment 2nd ed Philadelphia Lippincott Williams and Wilkins 2000 ISBN 0781712009 Internal source of pressurised gas Most commonly the internal source of pressurised gas makes use of air and oxygen from the hospital central supply The two gases are mixed by a blender to achieve the desired oxygen concentration FiO2 while the gas pressure from the wall is appropriately reduced by pressure reducing valves The internal source is thus ready for gas delivery to the patient Inspiratory valve expiratory valve and ventilator circuit These elements represent the actuators of positive pressure ventilation In the basic operating mode the two valves work with a synchronised but opposite phase while one valve is open the other is closed and vice versa The ventilator circuit consists of large bore tubes mostly external to the ventilator and includes an inspiratory limb an expiratory limb and a connecting Y piece Between the Y piece and the patient interface tracheal tube or mask a short flexible tube catheter mount is normally used representing a common airway through which the gas passes to the patient during inspiration and returns during exhalation During the inspiratory phase the inspirat
109. ts illustrates a complete approach to the analysis of respiratory dynamics in a ventilated patient and the importance of a patient centred serial approach to optimisation of the mechanical respiratory support However remember that achieving favourable results with such a multifaceted approach is complex and continued attention to detail will be required as things may change rapidly in the clinical setting By continuing these processes in this instance you were able to successfully wean the patient from mechanical ventilation The underlying disease improved during this time but remember however that recovery can take time Finally always consider that in most cases mechanical ventilation is a symptomatic treatment Never forget the treatment of the underlying condition s 75
110. ur elements summarised below PHYSIOLOGICAL PRIMARY LUNG TIMING GENERAL TASKS TO MANAGE DISEASE APPROACH CO elimination lo lung disease et Aggressive amp Oxygenation do Assista nce of Obstructive respiratory De muscles a weaning E anced In a given clinical context more than one choice can be clinically acceptable Consensus is more frequent with regard to what should be avoided rather than what should be selected Also the choice necessarily depends on the equipment usually used in that clinical setting as well as on the experience of the staff Initiating ventilator support In less severe cases when there is no independent indication for intubation the initial support can be performed with pressure support ventilation PSV delivered by mask In more severe cases and when mask ventilation fails intubation is necessary and support will be initiated with volume controlled ventilation VCV or pressure controlled ventilation PCV The traditional initiation with VCV is not essential When oxygenation is severely compromised ventilation should be started with an FiO of 1 while PEEP when indicated should be progressively escalated Escalation and maintenance When mask ventilation is successful maintenance involves continuous or intermittent PSV by mask In intubated patients according to the severity of lung disease associated diseases the need for sedation and respiratory muscles status
111. ut when breathing 100 oxygen a ventilation perfusion mismatch in itself should not cause oxygenation impairment Lumb AB editor Nunn s Applied Respiratory Physiology 6 edition Elsevier Butterworth Heinemann Philadelphia 2005 ISBN o 7506 8791 6 LEARNING SSUES Ventilator monitor See also the PACT module on Respiratory monitoring Q What parameters do you need from the ventilator to obtain a respiratory mechanics profile of the patient respiratory system compliance respiratory system resistance and PEEPI A Itis necessary to perform an inspiratory and expiratory occlusion manoeuvre to obtain the plateau and peak inspiratory airway pressures Vt and inspiratory flow during VCV and total level of PEEP Q On the ventilator you measure Vt 700 ml Inspiratory Flow 0 6 L sec PEEPI 1 cmH 0 Peak inspiratory airway pressure 40 cmH 0O and plateau inspiratory pressure 34 cmH2O Compute respiratory mechanics parameters A Vt is 700 ml PEEPi 1 cmH20 The pressure necessary to counteract the elastic property of the respiratory system is Plateau pressure PEEP PEEPi 37 10 1 26 cmH 0O The respiratory system compliance 700 26 27 ml cmH 0 Inspiratory flow 0 6 L sec The inspiratory flow driving pressure is Peak pressure Plateau pressure 3 cmH O Thus the respiratory system resistance is 3 0 6 5 cmH O L sec 62 Patient Challenges LEARNING SSUES Choice of tidal volume and
112. ventilation is of paramount importance for the successful and safe use of ventilators in the full variety of critical care situations and is a core element of critical care practice In the online appendix you will find four original computer based interactive tools for training in mechanical ventilation Additional illustrative materials are available online 1 Task 1 The nature of respiratory failure 1 THE NATURE OF RESPIRATORY FAILURE Respiratory failure is usually classified as pump failure failure of ventilatory function which is termed type 2 failure or as lung failure failure of the lung parenchyma often termed type 1 failure Pump failure or lung failure The respiratory system can be modelled as a gas exchanger the lungs ventilated by a pump Dysfunction of either pump or lungs can cause respiratory failure defined as an inability to maintain adequate gas exchange while breathing ambient air RESPIRATORY FAILURE dysventilation pump failure lung failure intrinsic fatigue EN alveolar airway vascular dysfunction load dysfunction obstruction dysfunction high impedance and or high ventilation requirement Pump failure and lung failure rarely occur in isolation in intensive care patients Frequently a patient alternates between prevalent pump failure and prevalent lung failure during the course of their illness Pump failure Pump failure primarily results in alveolar hypoventilation Pump
113. ventional ventilation modes e Volume Controlled Ventilation VCV In this mode the tidal volume Vt is pre set Breaths are either controlled or assist controlled depending on the lack or presence of spontaneous inspiratory activity and on whether or not the inspiratory trigger is active Inspiration takes place according to the principle of the instantaneous control of flow When the inspiratory trigger is active VCV is known as Assist Control Ventilation ACV e Pressure Controlled Ventilation PCV In this mode the tidal volume is delivered by a pre set pressure Breaths are either controlled or assist controlled depending on the lack or presence of spontaneous inspiratory activity and on whether or not the inspiratory trigger is active e Pressure Support Ventilation PSV In this mode spontaneous breaths are assisted by a pre set pressure e Spontaneous breathing with CPAP All breaths are spontaneous and the inspiratory pressure is ideally equal to the set PEEP level Technically when applied with a mechanical ventilator spontaneous breathing with CPAP is identical to PSV with a pressure support of zero Alternatively this mode can be applied with a freestanding continuous flow circuit independent from the ventilator wall CPAP e Synchronised Intermittent Mandatory Ventilation SIMV This mode alternates assist control volumetric inflations delivered according to a user set mandatory frequency and breaths that can be

Mechanical ventilation - PACT

Contents

Download Pdf Manuals

Related Search

Related Contents