Less isoflurane is required after than before cardiopulmonary bypass to maintain a constant bispectral index value.
OBJECTIVE: To test whether patients require less volatile anesthetic after cardiopulmonary bypass (CPB). DESIGN: Prospective, observational clinical study. SETTING: Cardiovascular operating rooms of a large teaching hospital. PARTICIPANTS: Twenty adult patients undergoing surgery with CPB. INTERVENTIONS: Subjects received a computer-controlled fentanyl infusion designed to maintain effect site concentrations of 3 ng/mL, combined with a variable amount of isoflurane. MEASUREMENTS AND MAIN RESULTS: The end-tidal isoflurane concentration associated with a target bispectral index of 55 was recorded during skin preparation, after sternotomy, during rewarming, and after separation from CPB. Adjusted, geometric mean (95% confidence intervals), end-tidal isoflurane concentrations associated with a bispectral index of 55 were 0.46% (0.38% to 0.58%) during skin preparation, 0.47% (0.39% to 0.58%) after sternotomy, 0.35% (0.29% to 0.42%) during rewarming, and 0.36% (0.31% to 0.43%) after separation from CPB. The last 2 concentrations (recorded near the end and after CPB) were significantly (p < 0.05) less than the first 2 concentrations (recorded before CPB). CONCLUSION: Because the level of surgical stimulation was relatively constant and minimal at the times of the measurements, these results are consistent with a reduced need for isoflurane after compared with before CPB.