In Vitro Validation of the Affinity NT Oxygenator Arterial Outlet Temperatures

Background: During cardiopulmonary bypass, the rates of cooling and rewarming and the maximum temperatures attained are implicated in patient morbidity. Thus, accurate oxygenator arterial outlet temperature measurements are needed. The purpose of this study was to determine the accuracy of the arterial outlet temperature probe on the “Affinity NT” membrane oxygenator in measuring perfusate temperatures.

Methods: An in vitro circuit was used. Crystalloid solution was recirculated through an Affinity NT membrane oxygenator and, to simulate the patient, a second oxygenator. Water was recirculated through the heat exchanger of the second oxygenator via a reservoir. A myocardial temperature probe was inserted in-line 4 cm distal to the Affinity NT oxygenator arterial outlet temperature probe and was considered to measure the actual temperature of the perfusate. Temperatures were simultaneously recorded from the in-line probe, arterial outlet probe, and reservoir every second. Twenty-seven trials were run using random combinations of three Affinity NT oxygenators and three in-line probes. Each trial entailed cooling an initially normothermic reservoir to 28 degrees C and then rewarming it to normothermia again.

Results: The arterial outlet temperature probe on the Affinity NT membrane oxygenator underestimated the perfusate temperatures during early rewarming (bias of 0.72 degrees C; precision of +/-1.15 degrees C) and late rewarming (bias of 0.52 degrees C; precision of +/-0.97 degrees C).

Conclusion: An overestimation of the perfusate temperatures occurred during early cooling (bias of -0.57 degrees C; precision of +/-1.37 degrees C). Only during the late cooling phase was the arterial outlet temperature probe accurate (bias of -0.02 degrees C; precision of +/-0.3 degrees C). The perfusionist should be aware of the temperature probe monitoring characteristics of the oxygenator to safely perfuse the patient.