Patient with aortic stenosis and coronary artery disease for AVR+CABGx2(LIMA+SVG).
Patient details: Height 179 cms, Weight 111 kg, Cardiac Output 5.5LPM with cardiac index of 2.4.
Pre-op Hb 14.4g/dl
Prime Volume 800mls Hartmanns, 5000IU Heparin, 4mmol Magnesium
APP/RAP carried out, target temp 32 degrees Celsius.
CO2 flushing at 5LPM was being utilised, this was reduced upon pCO2 increase to help attenuate to no avail.
Details of Incident
The first 60 mins of bypass were uneventful with average pO2’s of 25kPa. Approximately 60 mins into CPB patient pO2 and pCO2 began to fall/rise respectively. Sweep gas and FIO2 were increased to compensate. However both pO2 and pCO2 were out of protocol range despite running a sweep of 9LPM and FIO2 of100%.
A 20L gas blender was inserted into the circuit to compensate, a sweep of 15 LPM was required to attenuate pCO2.
pO2 remained below protocol minimums however they were within physiological normal range (for the whole case, the lowest pO2 recorded was 11.35kPa).
Venous saturation dropped to below 60% and lactate slowly increased. Pump flows averaged 100% throughout.
Hb averaged 12.65g/dl, DiO2 387m/min/m2 and ACT’s were above 400 seconds and any drops were treated with 5000 IU heparin (lowest ACT on bypass 379 seconds). Transmembrane pressures were not measured as the unit routinely uses centrifugal pumps. The RPM flow rate did not decrease, nor was there any indication of clot formation upon inspection of oxygenator post CPB.
The issues being experienced were communicated with the surgeon and the potential need for an oxygenator changeout was discussed. The surgeon was close to removing the cross clamp and the decision was made to wait. Once the cross clamp was removed, ventilation was resumed and the heart was allowed to eject. Blood gases and venous saturation began to slowly improve until CPB was terminated
Liva Nova 6F Oxygenator
20L gas blender was inserted to attenuate high pCO2. Replacement oxygenator was statically primed should there have been a further drop in oxygenation status, thus prompting a change out. Ventilation was resumed after removing of the cross clamp and the heart was allowed to eject for the duration until CPB had been terminated.
Consideration was given to a gas filter failure and the filter was removed to no avail.
The oxygenator was retained and sent back to Liva Nova for investigation.
Post-operatively, there was some speculation within the department that it may not have been the oxygenator but rather a hypermetabolic state, specifically malignant hyperthermia (MH), however the only indication on CPB was hypercarbia requiring a large amount of sweep to correct and falling venous saturation despite a physiologically normal pO2 as per Butala et al.2018.
Patient temperature did not rise acutely but this would have been confounded with the use of a heater cooler. The patient did not present with symptoms of MH on induction of anaesthesia and no dantrolene was administered.
Post event the patient was sent for MH testing-awaiting update on results.
Upon reflection what do you think went well?
The decision not to change out the oxygenator and to wait until the cross clamp came off to allow the heart to eject.