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Less isoflurane is required after than before cardiopulmonary bypass to maintain a constant bispectral index value
J C Lundell1, P E Scuderi, J F Butterworth
1Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, NC, USA.
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.