During use of the Affinity Fusion Oxygenators high pre-membrane pressures were observed. Fifteen minutes into bypass and whilst cooling to 32degrees, the pre-membrane pressures of 380mmHg were climbing to 500mmHg. The target patient blood flow was 5.6LPM (relatively large patient). The pressure isolators and equipment were checked. As pressures were continuing to rise a second opinion was sought and the decision was taken to change out the oxygenator.
At that stage (20mins in to bypass, maximum revolutions per minute on the centrifugal pump (3500RPM) could only maintain a flow to the patient of 3.5LPM approximately. Blood gas was performed and the patients parameters were still okay. The patient was not yet cross clamped and cardioplegia had not been given. The anaesthetist ventilated the patient while the perfusionist changed out the oxygenator (approximately 5 minutes to changeout the oxygenator, done in a controlled manner as the patient was stable).
Upon initiating bypass with a new (second) oxygenator, high pre-membrane oxygenator pressures were noted. The high pressure alarm was set off at 550mmHg. A flow of approximately 5.2LPM was maintained and the blood gas results of the patient were acceptable. The second period of bypass was around 2hours long. As the patient was being rewarmed toward the the end of bypass, the pre-membrane pressure started to falling to normal levels (330mmHg pre and 210mmHg post membrane). During both bypass periods the ACT's were good (>480 on Medtronic ACT plus).
A HMS Hepcon heparin management system was used. This patient had a target heparin concentration of 3mg/kg. Despite ACT's being good the HMS results stated to provide more heparin (anti-coagulate the patient more). During the bypass an additional 20,000units of heparin were given. The patient's Hb was 150g/liter, but the perfusionist did try and run at slightly lower of 120g/liter. There were no known patient blood anomalies prior to bypass. The patient was given Aprotinin and additional Aprotinin at the end of bypass (prescribed - as had passed the allergy check).
This is one of 8 recent HPE with this oxygenator this year (2021). We have been using them for a number of years without similar problems prior to these events.
Medtronic Affinity Fusion Oxygenator