Potential problem when using the new lower-prime hollow-fibre membrane oxygenators with uncoated stainless steel heat exchangers.

A prospective study was conducted to evaluate the trans-oxygenator pressure gradient across three different hollow-fibre membrane oxygenators during routine cardiopulmonary bypass (CPB). Sixty consecutive open-heart surgery patients were randomly divided into three groups each receiving a different model of membrane oxygenator. Inlet and outlet pressures, as well as patients' pressures, blood flow, revolutions per minute and tympanic membrane temperature were recorded every 15 min during CPB. Within the study groups, there were subsets of patients who exhibited high trans-oxygenator pressures. Although most of these episodes were transient and resolved over a period of time, there were several cases during which the high trans-membrane pressures persisted, resulting in decreasing oxygenator performance. In one such case, oxygenator change-out was required. After extensive analysis and review, the only similarities or correlation that could be made were with the marriage of the newer lower-prime hollow-fibre membrane oxygenators (with corresponding narrow blood path) and the integral uncoated stainless steel heat exchangers. Further study needs to be performed to pinpoint the mechanism and pathophysiology that are involved in this phenomenon.