Isoflurane elimination via a bubble oxygenator during extracorporeal circulation.

It has been suggested that inhalational anesthetics should be discontinued at least 15 minutes prior to termination of extracorporeal circulation (ECC) to avoid myocardial depression. However, data regarding elimination of inhalation agents via a bubble oxygenator from hypothermic, hemodiluted patients have not been previously reported. The washout of isoflurane (ISF) from ten cardiac surgical patients using mass spectrometry was studied. The mean baseline oxygenator exhaust concentration of ISF was 0.85% prior to termination of ECC. Oxygenator concentration of ISF decreased to less than 0.05% in 8.8 +/- 2.5 minutes. Eight of ten patients had ISF washout curves best characterized by a one-compartment model, with a mean time constant of 1.94 minutes. Therefore, 95% washout of ISF should occur in 5.8 minutes (three time constants). It is suggested that ISF may be used closer to the termination of ECC than previously recommended without fear of significant myocardial depression.