Pentazocine increases bispectral index without surgical stimulation during nitrous oxide-sevoflurane anesthesia

Although there have been a large number of reports on the effects of opioids on the bispectral index (BIS) during anesthesia, the effects of pentazocine on the BIS have not been reported. In this study, 60 patients scheduled for elective oral surgery [30 females, 30 males; all American Society of Anesthesiologists Physical Status (ASA PS) category 1] were enrolled in the trials. Maintaining gender parity, we randomly assigned the patients to one of three groups: pentazocine group (0.3 mg/kg; n = 20), fentanyl group (1 μg/kg; n = 20), or saline group (n = 20); these opioids were administered intravenously 15 min after the intubation. Anesthesia was induced with thiopental and vecuronium bromide and maintained with nitrous oxide (4 l/min)-oxygen (2 l/min)-sevoflurane (1%). At 15 min after the intubation, mean arterial blood pressure (MAP), heart rate (HR), and BIS index were recorded as baseline values. MAP, HR, and BIS values were measured at 2.5-min after the intubation up to 30 min. All data were expressed as the mean ± standard deviation. Differences in BIS values, MAP, and HR among the three groups throughout the experiment were analyzed using two-way repeated-measures analysis of variance (ANOVA), and demographic data among the three groups were analyzed using one-way ANOVA. Post hoc comparisons were performed using Fisher's protected least significant difference test. A P value of <0.05 was considered to indicate statistically significance. MAP and HR showed no significant differences among the three groups during the study. BIS values significantly increased between 5 and 15 min after the intubation relative to the baseline value in the pentazocine group (P < 0.001), and BIS values in this group were significantly during this time period than those in the fentanyl and saline group (P < 0.001). BIS values were not significantly different between the fentanyl group and saline group. These results indicated that pentazocine, but not fentanyl, under nitrous oxide-sevoflurane anesthesia caused a statistically significant increase in BIS in our patients.