Should the gas outlet port on membrane oxygenators be routinely scavenged during cardiopulmonary bypass?

Elimination of a volatile anesthetic agent administered prior to the start of bypass through the oxygenator has not been previously described. The purpose of this study was to determine the contamination risk from enflurane used before but not during cardiopulmonary bypass. Enflurane concentration was measured from the gas outlet port of a membrane oxygenator using infrared gas analysis in 11 cardiac surgical patients. The mean peak concentration at the gas outlet port in patients who had a final end-tidal concentration of < or = 0.3% was 0.08 +/- 0.04%, compared to 0.18 +/- 0.05% in patients with a final end-tidal concentration of more than 0.3%, P < 0.001. The elapsed time to reach peak concentration was 8.3 +/- 8.4 minutes, whereas the elapsed time from the peak concentration to 50% of the peak level was 63.1 +/- 25.1 minutes. At the time of peak enflurane release, a concentration of less than 2 ppm was measured at distances of 10 cm or less from the oxygenator gas outlet port in patients with an end-tidal enflurane of < or = 0.3%. In one patient with a final end-tidal enflurane of 1.1%, a contaminant level of 2 ppm could be measured at 95 cm from the oxygenator gas outlet port. This demonstrates that there is a potential risk of contamination from volatile anesthetics used immediately prior to extracorporeal circulation. Minimizing this risk may necessitate routine scavenging of the oxygenator, or simply avoiding increased concentrations of inhalation anesthesia before initiating cardiopulmonary bypass.