In vivo uptake and elimination of isoflurane by different membrane oxygenators during cardiopulmonary bypass

Background: Volatile anesthetics are frequently used during cardiopulmonary bypass (CPB) to maintain anesthesia. Uptake and elimination of the volatile agent are dependent on the composition of the oxygenator. This study was designed to evaluate whether the in vivo uptake and elimination of isoflurane differs between microporous membrane oxygenators containing a conventional polypropylene (PPL) membrane and oxygenators with a new poly-(4-methyl-1-pentene) (PMP) membrane measuring isoflurane concentrations in blood. Methods: Twenty-four patients undergoing elective coronary bypass surgery with the aid of CPB were randomly allocated to one of four groups, using either one of two different PPL-membrane oxygenators for CPB or one of two different PMP-membrane oxygenators. During hypothermic CPB, 1% isoflurane in an oxygen-air mixture was added to the oxygenator gas inflow line (gas flow, 3 l/min) for 15 min. Isoflurane concentration was measured in blood and in exhaust gas at the outflow port of the oxygenator. Between-group comparisons were performed for the area under the curve (AUC) during uptake and elimination of the isoflurane blood concentrations, the maximum isoflurane blood concentration (C-max), and the exhausted isoflurane concentration (F-E). Results: The uptake of isoflurane, expressed as AUC of isoflurane blood concentration and a function of F-E, was significantly reduced in PMP oxygenators compared to PPL oxygenators (P < 0.01). C-max was between 8.5 and 13 times lower in the PMP-membrane oxygenator groups compared to the conventional PPL-membrane oxygenator groups (P < 0.01). Conclusions: The uptake of isoflurane into blood via PMP oxygenators during CPB is severely limited. This should be taken into consideration in cases using such devices.