PH-11060 Phoenix Mass Balance System Description and
Contents
1. Rev A FORM TAA FRM 0042 Effective 10 08 2008 P2 FLOW is the dialysate flow ml min through pump P2 as controlled by D2 It is important to understand that P2 flow is a calculated value not a measured value It is calculated based on the pump speed the frequency read from the encoder on the pump and the pressure across the pump head or delta A pressure The PO pressure transducer measures the pump inlet pressure and the PD transducer measures the outlet pressure PD PO PA Generally speaking it is easier for P2 to pump fluid the pump frequency will be lower when the inlet pressure is positive with respect to the outlet pressure and more difficult when the outlet pressure is higher It is more difficult for the P2 FLOW value to stabilize when the delta pressure is near zero The P2 pump frequency is displayed as P2 FREQ Calibrating P2 involves controlling the delta pressure and allowing the software to measure the frequency that delivers the commanded dialysate flow rate as measured by D2 D1 FLOW should equal D2 FLOW P2 FLOW should equal D2 FLOW the UF rate Example Dialysate flow set to 800 ml min Ultrafiltration rate set to 9 Kg Hr or 15 g min DIAL FLOW should read 800 D2 FLOW should read 800 P2 FLOW should read 815 Mass Balance Deviation Long MBAL LONG MB Long is the amount of drift between D1 and D2 since the last D2 calibration D2 is calibrated with respect to D1 using fresh water not dialysate MB Lon2. GAMBRO Gambro Renal Products Technical Assistance Services http tech usa gambro com 800 525 2623 303 232 6800 Technical Update PH TR 11060 12 2008 TROUBLESHOOTING Equipment Type Phoenix Dialysis System Su bj ect Phoenix Mass Balance System Description and Troubleshooting From Don O Connell Overview of Phoenix Mass Balance For a flow controlled dialysis system to accurately regulate and monitor fluid removal from the patient it is critical that the dialysis system ensures that the volume of dialysate entering and leaving the dialyzer is exactly the same In addition the system must also ensure that the added volume of fluid exiting the dialyzer contributed by the ultrafiltrate from the patient is accurately controlled and measured separately The Gambro Phoenix measures and controls the amount of fluid entering the dialyzer with a flow meter D1 It then uses a second flow meter D2 to measure and control the fluid exiting the dialyzer This system is what we refer to as mass balance It is not necessary that the flow meters precisely measure the actual volume of the dialysate the specification is 500 10 ml min but they must be in exact agreement with each other Initially D1 is calibrated so that it controls the P1 pump to deliver 500 10 ml min of water to the drain Then D2 is calibrated so that its displayed flow exactly matches D1 s displayed flow Inside of the flow meter body are two el
3. alarm Version 3 35 does stop the Dialysis Time counter whenever the machine is in bypass conductivity temperature or pH alarms as well as taration and also blood related alarms This includes both the routine and the extended tarations As a result there is typically a greater disparity between Treatment Time and Dialysis Time with version 3 35 SW than with 3 34 SW Rev A FORM TAA FRM 0042 Effective 10 08 2008 Troubleshooting Mass Balance Alarms 343 Flow meter Drift Check the value of Mass Balance Deviation Long The Flow meter Drift alarm occurs when MB Long is greater than 2 5 The display reads 25 A chemical disinfection using bleach or a heat citric disinfection may result in a significantly lower MB Long D1 is more likely to be affected by precipitate D2 by protein buildup Heat citric disinfection is good for both bleach for protein Mass Balance Long is recalculated during Dialysate Preparation Hyd Phase 10 following the T1 test completion If disinfection doesn t help perform the D1 and D2 Tests and recalibrate as necessary A good rule of thumb is to recalibrate the flow meters when the first MBL value calculated after disinfection is greater than 12 If a flow meter cannot be calibrated replace it Observe the bar graph during the D1 and D2 Test Ideally the bar graph should increment steadily to 100 and stay there If the bar graph is unstable and a replacement flow meter behaves the same way it s likely t
4. will increase the discrepancy between the timers Tarations are not the only reason for the difference between treatment time and dialysis time Any alarm that puts the machine in bypass stops the dialysis timer An empty acid jug or Bicart will stop the timer until the concentrate is replaced and the conductivity stabilizes Whenever the blood pump stops the timer stops Repeated venous or arterial pressure alarms will significantly increase the difference between treatment and dialysis times When investigating an operator complaint that the Dialysis Time is significantly different from the Treatment Time note the current value of Mass Balance Long A large value may indicate the need of a bleach disinfection to remove accumulated protein from D2 or a descaling to remove precipitate from D1 It may also result from flow meter drift over time that requires flow meter calibration The date that D2 was last calibrated can be seen on the Calibration page From the CAL HOME page after entering the password select D2 FLOWMETER and then the INFORMATION key The Last Calibration Date is displayed in the European format day month year Test D1 and D2 At the 500 setting D1 must deliver between 490 and 510 ml min At the 500 setting D2 should read 490 to 510 at the 750 setting D2 should read 735 to 765 to meet specifications For practical purposes there will be fewer problems if all readings are within less than 5 ml min of the set value Rev A F
5. ORM TAA FRM 0042 Effective 10 08 2008
6. bility of these alarms is significantly increased in this situation It was discovered that with version 3 34 software a false Error 144 alarm would be generated in the unique situation of a dialysate flow rate of 350 ml min selected and an ultrafilter in use This is corrected in version 3 35 P2 The P2 attribute results when the P2 pump reading does not match the flow meter readings It must agree within 60 ml min at a dialysate flow of less than 750 ml min and within 8 at a flow greater than 750 ml min 8 of 800 ml min is 64 ml min Keep in mind that P2 flow includes ultrafiltrate so it should be higher than D1 and D2 flow Rev A FORM TAA FRM 0042 Effective 10 08 2008 P2 flow depends on PO and PD readings so verify their accuracy P2 flow also depends on the pump encoder If the phonic wheel is loose or rubbing on the optical sensor the reading won t be accurate Perform the P2 Test and recalibrate if necessary If the message Components Out of Range appears repeat the calibration make sure there s water in the P2 test tool It should be about half full If the same message appears again replace the pump When testing or calibrating P2 if the water level in the P2 test tool does not stabilize the chamber fills up or empties out a Calibration Tool Error message may result The cause could be the P2 tool itself leaking or clamped line It could also be caused by a leak in the Phoenix hydraulics For exampl
7. e a leaking EVUFO valve Check the area around PI and PO The patient circuit section of the hydraulics can be pressure tested as described in ITM 9068 Phoenix T1 Test 16 Troubleshooting Probably the most common cause of an unstable water level in the P2 tool is failed or miscalibrated pressure transducers Another possibility is the situation where P1 and P2 are mismatched For example P1 is a worn old style pump and P2 is a new pump P2 may pull fluid out of the tool faster than P1 can put it in 309 Flow Balance Inaccurate This alarm is displayed after ten Flow Balance Error 144 alarms Dialysis Time Lagging Treatment Time The operator of the machine can choose how to determine that the treatment is complete If Treatment Time is selected the timer will count down from the time selected e g 4 Hours without interruption If Dialysis Time is chosen the Dialysis timer will stop whenever the blood pump stops or the machine is in bypass As mentioned above with version 3 35 software the dialysis timer now stops while the machine performs a taration An ordinary taration takes 40 seconds and occurs about every 15 minutes During a four hour treatment there would be 15 tarations taking a total of about 10 minutes So best case the Dialysis timer will lag the Treatment timer by 10 minutes with 3 35 software If any of the tarations are judged to be invalid one or more extended tarations will occur in an effort to flush the flow meter This
8. g is calculated during Dialysate Preparation Hyd phase 10 using fresh dialysate It typically increases over time due to aging of the flowmeters It also increases from one treatment to the next due to protein accumulation on D2 and then drops back following a bleach disinfection at the end of the day The Status screen display is a percentage For example 14 is 1 4 MB Long gt 2 5 results in the protective system generating Warning Alarm 343 Flow meter Drift QD 2 5 350 8 75 ml min 500 12 5 ml min 600 15 ml min 700 17 5 ml min 800 20 ml min Table 1 Mass Balance Deviation Short MBAL SHORT The density of the dialysate flowing through D2 is different than the density of the dialysate flowing through D1 D1 is exposed to fresh dialysate whereas the D2 is exposed to dialysate containing proteins from the patient s blood Throughout the treatment the Phoenix performs a taration every 16 minutes During the taration the machine is put in Bypass for a short time approximately 40 seconds D1 controls the P1 dialysate flow and this same flow is directed to the inlet of D2 D1 is seeing fresh dialysate but due to the volume of the tubing feeding D2 D2 is seeing used dialysate as it does in normal operation The Protective System notes the difference between the D1 flow and the D2 flow It subtracts the already calculated value of MB Long and calculates the value due only to the different densities of the dialysate This va
9. hat P1 is the problem Since P1 is providing the flow to D2 during the D2 Test and also during taration an unstable P1 may also affect the D2 reading If D1 is calibrated D2 must be calibrated If D2 is calibrated P2 must be calibrated 144 Flow Balance Error This alarm has four possible attributes 1 Valves 2 D1 D2 3 P2 Pump 4 No Cal Valves and No Cal are not common failures Refer to the Phoenix service manual D1 D2 This attribute will be displayed when the Mass Balance Deviation value the difference between D1 and D2 readings exceeds 3 for at least 22 seconds See Table 2 above This alarm may be preceded by a 343 alarm Troubleshooting and repair is the same as for the 343 alarm No flow meter reading or erratic readings may result from wiring connection problems NOTE At some facilities the machine is set up at a low dialysate flow rate in order to save on concentrate When the patient is connected the operator increases the dialysate flow Both Error 144 and Error 343 are generated based on percentage of error See Table 1 and Table 2 above Since the error is likely to be greater at a higher dialysate flow the percent of error allowed is greater But the software acquires the dialysate flow value during Setup If the machine is set up at a dialysate flow of 350 ml min the Flow meter Drift and Flow Balance Error limits will be based on the 350 flow rate even though the treatment is run at for instance an 800 flow The possi
10. ifies the Master that the coefficient just calculated is invalid The first coefficient calculated after Patient Connect is always considered invalid A second taration ensures validity If the dialysate flow rate is changed by the operator during the taration the calculated coefficient is not valid Normally the Master requests a taration about every 15 minutes during dialysis The number of seconds that have elapsed since the start of the previous taration can be seen on the second status page column D 34 as INTER CALIB Under normal circumstances this counter can be observed to count up to 960 and the machine will then be commanded into phase 18 The hydraulic phase can be seen on the first status page at the bottom of column A If the coefficient calculated is determined to be invalid the Master can force up to 3 extended tarations 90 seconds per taration before a mass balance alarm will occur Three 90 second tarations would result in a total of 4 minutes These extended tarations function to flush D2 and are intended to remove the accumulated deposits that caused the failed taration If the machine generates a Mass Balance alarm or goes into Bypass a taration is performed If the dialysate flow is changed a taration is performed Version 3 34 SW did not interrupt the Dialysis Time counter during a taration the Dialysis Time counter did stop when in bypass in response to an alarm condition or the blood pump stopped in response to an
11. liptical shaped gears Fluid rotates the drive gear which in turn drives the driven gear At the end of the driven gear is a magnet When the magnet passes a hall sensor built into the flow meter body an electrical pulse is generated One pulse corresponds to flow measured in microliters This is the calibration coefficient marked on the flow meter body The frequency of the flow meter signal is used to calculate the flow rate There are a number of factors that affect the calibration of the flow meters Over time the gears may not spin as freely as they did originally so the flow displayed is slightly lower than the actual Rev A FORM TAA FRM 0042 Effective 10 08 2008 flow The readings may change temporarily due to precipitate or protein build up and then revert to the original reading following a descaling or bleaching To ensure that the flow meters are in agreement the Phoenix performs a taration Just as we tare a scale zero it with no weight applied the flow meters are tared regularly Typically the Phoenix performs a taration shortly after a dialysis treatment is initiated when the PATIENT CONNECT key is selected and then about every 15 minutes after that Also a taration occurs after the machine is put in bypass whenever the dialysate flow rate is changed and following a mass balance alarm During a taration Hydraulic phase 18 the machine is placed in bypass EVDS1 is de energized and EV2 is closed The P1 dialysa
12. lue is recorded as Mass Balance Deviation Short 3 Rev A FORM TAA FRM 0042 Effective 10 08 2008 The Status Screen display is a percentage It is typically updated every 16 minutes when the Phoenix performs its scheduled taration No alarms are generated based on the value of MB Short Mass Balance Deviation MBAL_DEV The Protective System monitors the difference between the flow measured by D1 DIAL FLOW and the flow measured by D2 D2 FLOW From this difference it subtracts the previously recorded values of MBal Long and MBal Short The resulting value is referred to as Mass Balance Deviation This Status Screen is also displayed as a percentage Mass Balance Deviation is the value which triggers Alarm 144 Flow Balance Error When in Dialysis the Phoenix does not generate the alarm immediately but allows time for short term disturbances to settle down The amount of time that the machine waits before generating the alarm depends on the percentage of the deviation between D1 and D2 3 15 22 seconds 16 30 15 seconds gt 30 6 seconds QD 3 16 30 350 10 5 ml min 56 ml min 105 ml min 500 15 ml min 80 ml min 150 ml min 600 18 ml min 96 ml min 180 ml min 700 21 ml min 112 ml min 210 ml min 800 24 ml min 128 ml min 240 ml min Table 2 3 34 Versus 3 35 Software For the following discussion we ll define these terms K Kappa value K 1 Previous Kappa measurement K 2 2 Previous Kappa measu
13. rement In Version 3 34 software the conditions for acceptance of a calculated K coefficient are 1 0 50000 lt K lt 1 50000 and 2 K K 1 lt 0 00305 where K 1 is the calibration factor computed in the previous calibration phase That is the K value when calculated must be greater than 0 50000 and less than 1 50000 The difference between the current K measurement and the previous K measurement must be less than 0 00305 In Version 3 35 software the conditions for acceptance a calculated K coefficient are 1 0 50000 lt K lt 1 50000 and 2 K K 1 lt 0 00305 or K K 2 lt 0 00305 Rev A FORM TAA FRM 0042 Effective 10 08 2008 where K 1 and K 2 are the calibration factors computed in the previous calibration phase and the second previous calibration phase and 3 The calibration coefficient shall also meet the following condition K K 1 lt 0 00100 That is the K value when calculated must be greater than 0 50000 and less than 50000 The difference between K and K 2 must be less than 0 00305 The difference between K and K 1 must be less than 0 00100 The Hydraulic slave performs a flow meter cal when commanded by the Master K D1 pulses D2 pulses If D1 gt D2 then K is gt 1 These pulse counts can be seen on the second status screen page Column A 29 and 30 as DI COUNTER and D2 COUNTER If the value calculated does not meet the above conditions the Hydraulic slave not
14. te flow controlled by D1 is directed to the inlet of D2 D1 is exposed to fresh dialysate and because of the volume of the fluid contained in the tubing supplying D2 D2 is exposed to the same effluent that it normally sees during a treatment The software measures the difference between the two flows and calculates the number that when multiplied by the D2 flow equals the flow measured by D1 This fudge factor is called K or Kappa It is displayed on the first Status Screen page as KAPPA _FM Ideally D1 is exactly equal to D2 and therefore K 1 000 If D2 measures less than D1 K will be greater than 1 If D2 measures more than D1 K will be less than 1 The D2 flow measurement will be multiplied by this value of K until the next taration at which time K is recalculated During the taration there is no dialysate flow to the dialyzer but ultrafiltration is not interrupted P2 controlled by the PO and PD pressure transducers continues to run and the ultrafiltration pump PUF continues to remove fluid from the patient at the programmed UF rate Dialysate Flow in Taration EVUfo em From Dialyzer To PUF Status Screen Information In addition to the K value the first page of the Status Screens displays other information related to the mass balance system DIAL FLOW is D1 flow ml min D2 FLOW is D2 flow ml min D1 FLOW should equal D2 FLOW D1 KD2 is the difference between D1 flow and the corrected D2 flow 2
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