The Journal of ExtraCorporeal Technology No 56-4 | Page 67

A . Svec et al .: J Extra Corpor Technol 2024 , 56 , 203 – 206 205

Table 1 . Distinct differences and similarities of the Medtronic Affinity NT Fusion and Terumo FX25 Oxygenator .

( Terumo Cardiovascular , Ann Arbor , MI ) oxygenator instead of a Medtronic Affinity Fusion .

After completion of the hemiarch replacement , CPB was resumed , and the patient was rewarmed . With the Terumo FX25 oxygenator , the flows increased to 6.15 L / min at 2801 RPMs with 182 mmHg resistance . The blood pressure was 73 mmHg . At 1016 another TEG was completed . At this time the platelet count was 17,000 / mL . During the case , the TEG drifted more towards normal throughout the case and ended at 39.5 mm post bypass Blood gases were monitored through the rest of the case with no significant changes . Likewise , for the remainder of the case , the flows did not drop below 6.0 L / min . Following CPB , 200 mg protamine was given at 1105 , and ACT at 1110 was 126 .

Comment

Oxygenator HPE is a rare event that is associated with an incidence of approximately 0.4 – 2.3 % of cases [ 3 ]. In this case , the patient had a positive surgical outcome as is evident by a definitive aortic repair with next-day extubation and no documented neurological deficits . This successful result can be attributed to the quick intervention of the perfusion and surgical team . In retrospect and after the literature review , more troubleshooting should have been attempted before the oxygenator changeout . Epoprostenol administration and hemodilution could have been attempted to prevent the necessity for oxygenator changeout . In this case , however , rewarming the patient would not have been possible due to the necessity for DHCA . These troubleshooting steps were not part of our policy and procedure manual and were therefore not utilized . As a direct result of this case , epoprostenol administration , hemodilution , and patient rewarming have been added to our policy and procedures for HPE .

The calculated lean body mass for the patient was calculated to be 105 kg . This was not part of our standard of care to be calculated before the case . However , following the case , the proper flows according to the ELBM were calculated . To acquire a minimum of 2.0 CI , flows should be 4.6 L / min . With this now in mind , the patient only had flows below 4.6 L / min directly before the troubleshooting began . This supported our decision to only include one oxygenator . During the case , the perfusion team was unaware of the platelet decrease . The TEG showed at 0755 the platelet count was 214,000 . This was a 13.0 % decrease in platelet count from the preoperative labs to the first blood draw in the operating room . After another 261 min , the platelet count decreased by another 92.1 %, specifically to 17,000 . The observed decrease in platelet count may be explained by platelet aggregation at the oxygenator . This phenomenon is not a new discovery ; platelets are known to attach to the surface area of the oxygenator membranes [ 4 ]. The observed decrease in platelet count and plausible platelet aggregation is a potential leading cause of the HPE and the decreased flow of blood through the oxygenator .

The major difference between the Medtronic and the Terumo oxygenators was the blood flow path ( Table 1 ). The Medtronic oxygenator which has a radial flow design was first used in the circuit for this case . The inlet of the Medtronic is above the outlet ; therefore , blood must flow down through the oxygenator , parallel to the fiber bundle . Because of this longer flow path through the fiber bundle , the Affinity pump must pump against increased resistance to begin with .

This blood flow path in combination with the patient ’ s large BSA may be a plausible reason for the observance of HPE in this case . In circuits with oxygenators that feature lower resistance , HPE may not have been noticed as the RPMs could be turned up to a flow that would support the patient . Following the incidence of HPE in this case , the Medtronic oxygenator was changed to a Terumo transverse flow oxygenator . The inlet of this model is on the side and the outlet is at 90 ° to the inlet on the front of the device . Additionally , blood flows perpendicular to the oxygenator and therefore has a shorter flow path across the fiber bundle . This leads to less resistance from this oxygenator as evidenced by the ability to generate a higher flow at lower RPMs once the oxygenator was changed to the Terumo FX25 . Since studies in HPE have been completed on roller pumps , it is unclear whether these steps will resolve the issue completely in cases with centrifugal pumps , but they are nonetheless worth attempting if oxygenator changeout can be avoided [ 2 ]. While oxygenator changeouts due to HPE are not unique , it was notable that two Medtronic Affinity NT Fusion oxygenators had to be changed out in this case .

Funding This research did not receive any specific funding .

Conflicts of interest The authors declared no conflict of interest .