Pressure Transducer Incident
Op date 01/06/2026
AVR + ascending aortic repair (Bentall)
Height 183 Weight 102.9 Calculated flow5.39 BSA: 2.25
Pre-bypass Hb 130, lowest Hb on first bypass102.
Right innominate artery cannulation 20fg Select arterial cannula.
Right Atrium cannulated with 2-stage venous cannula
Left carotid cannulated with a retro cannula.
Lower body circulatory arrest: Innominate cerebral flow 22 mins
Left Carotid Perfusion: 18 mins
Core Temperature 25oC
Custodiol CPG
On bypass:
Pre-bypass pressure transducer: 444 mmHg Post bypass pressure transducer: 255 5.3 lpm RPM: 2878
Bypass initiated uneventfully and patient cooled to 25oC, flow from the main centrifugal pump via the right innominate artery at cardiac index of approximately 2.4.
Once distal end of conduit and coronary buttons attached, cross clamp went on for proximal end attachment, innominate cannula repositioned and vessel snugged for right cerebral flow and lower body circulatory arrest. Flow to the right innominate artery was 500-700mls/min initially.
Cerebral saturations on Hemisphere cerebral monitoring good, although demonstrated that the flow was preferentially favouring the left brain.
Retro cannula located in the left carotid artery for selective antegrade cerebral flow.
As cerebral flow to the left carotid artery was initiated on the roller pump to 100ml/min, high post membrane line pressure flagged on the arterial pump and pump RPM regulated as a result. Cannula location, line kinks/obstructions all checked.
Unable to resolve the high line pressure issue, operating surgeon requested that the flow be reduced on the arterial pump to 100ml/min and the right carotid flow on the roller pump be increased to 400ml/min.
Post membrane line pressure still high, pump regulating RPM due to this, flow low as a result, assistance requested from another perfusionist and 2 colleagues came in to help.
Pressure regulation limit on post membrane transducer increased with surgeons blessing but pump still regulating flow and pressure reading very high on the post membrane isolator.
Cerebral saturations remained ok on left and right hemisphere sensors, proximal graft attached and attempted to return to normal circulation, the post membrane pressures remained high at approximately 500mmHg, flow was approximately 1.5LPM.
Both pre and post bypass pressure transducers were zeroed by the primary perfusionist and again by a second perfusionist.
The post membrane pressure isolator was swapped to the pre membrane transducer (and vice versa) to check whether the pressure readings were correct.
It was noted later, on the electronic record that the readings on the Essenz record did not show this swap, the post membrane still read 500mmHg despite this now coming from the pre membrane and the pre membrane still read about 100 despite this now being attached to the post membrane isolator. It was also noted that the post membrane pressure did not drop to zero when the pressure isolator was removed.
All avenues explored which may contribute to high post membrane pressures, such as cannula position and possible dissection, both radials reading ok, as were the cerebral sats.
It was decided that a 2nd arterial cannula should be placed directly into the aorta in an attempt to bring the post membrane pressure down and improve flow, but this had no real effect.
The aortic cannula was removed to check the flow, and this was found to be low. The pump was still regulating rpm, the aortic safety clamp on the arterial line from the pump was opened to check if there were any flow restrictions caused by this device, no change to flow was observed.
Eventually the decision was made to bring in another CPB machine and swap out the first pump. Once switching to the new pump all the problems were resolved, and full arterial flow was achieved.
Blood from the first pump circuit was bagged up and re-infused to the patient via the new circuit.
The haemofilter from the original circuit was added to the new one and fluid was removed from the patient to increase haematocrit and remove additional prime volume.
Once bypass reinstated circulation remained stable on the new circuit with normal line pressures.
A second surgeon now scrubbed, tested the arterial cannulae independently for flow. The innominate cannula, a 20fg Medtronic Select was found to have half the flow of the 24fg EOPA cannula now located in the aorta directly, most likely that as it was a smaller cannula it would have required higher RPM from the arterial pump due to resistance.
A second perfusionist proceeded to rewarm the patient using only the aortic cannula. The remainder of the bypass progressed uneventfully.
Once fully rewarmed the patient was weaned from the pump.
After the case, the perfusion team attempted to replicate what had been happening on the first pump machine.
The isolators were returned to their normal positions and now appeared to be recording correctly and as expected, (the pump base had been turned off and back on again in the meantime).
It was noticed that a small amount of mannitol had leaked from the burette spike injection port and had found its way onto the transducer modules for pre and post membrane pressure isolators.
Looking back at the Essenz monitoring record it seems that the RPM on the Essenz had recorded as 1500 rpm a lot of the time even though in reality it had not been, the RPM was noted by 3 perfusionists at the time more like 2500-3500
The Essenz record showed that each time the control pressure threshold was increased, which regulates the RPM on the post membrane pressure transducer, the post membrane pressure would increase, but the flow did not. Possible runaway pressure transducer?
The pump was taken out of service, and the Liva Nova engineer was contacted. We were still unsure as to what could have caused the issue, and were concerned specifically about the pressure module, we reported our observations to the Liva Nova engineer who arrived the next day to inspect the pump base.
Conclusion
The engineer thoroughly checked the pump base and replaced the pressure modules and cables; he could not find a fault with the machine. He said he thought that it seemed like a runaway pressure module, unseen by him before, and that he suspected the mannitol spill may have contributed to this as the fluid could have got inside the pressure transducer and electronics.
He said that if the fluid had got inside the transducer housing, then it could have caused a change in the resistance valves of the circuit, hence changing the valve electronically and therefore the pressure reading, rather than by an actual pressure being applied to the transducer.
The engineer stated that any form of spillage can cause any number of problems, most unpredictable, and in this case, it seems that the fluid may have affected the pressure transducer circuit. Both transducers and cables were replaced with new, and the originals disposed of by the engineer during his inspection.
As it was only the pressure domes themselves that were swapped and not the cables at the time of the incident, the fault did not move. If it was a faulty transducer then swapping the cables around would have meant the fault changed channels. This would also have explained why swapping the pump fixed the issue.
The engineer recommended that if this type of issue were to occur again, then the cable should be removed from the pressure module, to prevent the regulation of RPM on the pump, and the pressure isolator dome moved to another module to assess true line pressure.
We were given the go ahead by the engineer to put the pump base back into service.
Patient was awake the following day and appeared unharmed.
