• C Roger Goucke, L Peter Hackett, P Hugh Barrett, and Kenneth F Ilett.
• Department of Anaesthesia, Sir Charles Gairdner Hospital, Nedlands, WA, Australia. roger.goucke@health.wa.gov.au
• J. Cardiothorac. Vasc. Anesth. 2007 Apr 1;21(2):218-23.

ObjectiveThe purpose of this study was to determine blood concentrations of enflurane delivered via a membrane oxygenator during hypothermic cardiopulmonary bypass (CPB) with changes in the input enflurane concentration and temperature and to characterize the pharmacokinetics of enflurane washout during and after CPB.DesignBlood enflurane concentrations were measured by gas chromatography before, during, and after CPB by using mean delivered enflurane concentrations of 0.5% v/v (group 1, n = 5), 0.8% (group 2, n = 7), and 1% (group 3, n = 14).SettingThe investigation was performed in a teaching hospital setting.ParticipantsTwenty-six patients undergoing cardiac surgery requiring hypothermic CPB.InterventionsVariations in input enflurane concentration in different patients plus blood sampling from the arterial side of the circuit for enflurane assay.Measurements And Main ResultsMedian (25th and 75th percentiles) pre-CPB blood enflurane concentrations were 48 (25-50) mg/L, 52 (47-56) mg/L, and 115 (90-143) mg/L in groups 1 (0.5% v/v), 2 (0.8% v/v), and 3 (1% v/v), respectively. During hypothermia (28 degrees C) corresponding enflurane concentrations were 44 (31-53) mg/L, 56 (45-62) mg/L, and 145 (109-203) mg/L, respectively. For groups 1 and 2, there were no significant changes in blood enflurane compared with the corresponding pre-CPB value. However, for group 3, cooling resulted in a significant increase (p = 0.006) in blood enflurane. In all groups, enflurane concentrations after rewarming were similar to those in the pre-CPB period.ConclusionsIt is concluded that exposure to enflurane concentrations greater than 0.8% during CPB can result in high blood concentrations.

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