A clinical comparison of bubble elimination in Quadrox and Polystan oxygenators

Background: Microbubbles generated during heart surgery on extracorporeal circulation have been implicated as a possible cause of postoperative neurocognitive dysfunction and negative outcome. The main sources of microbubbles in the extracorporeal circuit are air leaking from the venous cannulation site, air delivered by drug and volume administration, during the taking of blood samples, during hemofiltration, and by using vacuum-assisted venous drainage (VAVD). Membrane oxygenators, although not designed for the elimination of gaseous microbubbles, can eliminate much of this air. Aim of the study/hypothesis: The aim of this study was to test the hypothesis that the amount of microbubbles passing through the oxygenator varies depending on the oxygenator design. Methods: one hundred patients undergoing aortic valve replacement with cardiopulmonary bypass (CPB) were included in a retrospective clinical trial assessing the bubble elimination of the two oxygenators routinely used in our clinic. The oxygenators (Quadrox-iAdult/Polystan Safe Maxi) are manufactured with the same hollow-fiber material, but display different designs. Bubbles were detected by a two-channel ultrasound bubble counter. The probes were placed directly at the inlet and the outlet of the oxygenators. The filtration index was calculated by the bubble counter as a measure of the percentage reduction of bubble volume and number. Results: The Quadrox has a significantly higher filtration index (92.3% [ 89.7; 95.1], median [25(th), 75(th) percentile]) than the Polystan (74.9% [64.2; 80.9], p<0.001), indicating the superior ability of the Quadrox to eliminate microbubbles. Conclusion: Our study demonstrates major differences in the capacity of bubble elimination of the oxygenators being investigated, possibly depending on oxygenator design.