[Effect of pentazocine on the bispectral index during nitrous oxide-sevoflurane anesthesia].

The effect of pentazocine on the bispectral index (BIS) has not been reported. In this study, we have examined whether pentazocine alters the bispectral index during nitrous oxide-sevoflurane anesthesia. Thirty surgical patients were enrolled in this double-blind, randomized study. Anesthesia was induced with thiopental and vecuronium and maintained with nitrous oxide-sevoflurane with the bispectral index maintained at approximate 40. Under stable anesthetic condition before surgery, patients were assigned to receive either a bolus of pentazocine 0.3 mg x kg(-1), 0.6 mg x kg(-1) or the same volume of saline 15 min after induction. Blood pressure (BP), heart rate (HR) and BIS were measured every 2.5 min from 2.5 min before induction until 30 min after induction. BP and HR showed no changes after pentazocine administration compared with control group. BIS showed no significant change in the saline group, but it increased significantly in the pentazocine group. When pentazocine was administered 15 min after induction, BIS increased significantly 20, 22.5, 25, 27.5 and 30 min after induction compared with the control group. The increase of BIS by pentazocine showed no dose-dependent effect in our present study. We observed that intravenous pentazocine caused a significant increase in BIS under nitrous oxide-sevoflurane anesthesia. The depth of sedation should be assessed carefully using a bispectral index monitor when pentazocine is used together.