ABSTRACT
BACKGROUND: Although neuromuscular blockade can influence the bispectral index (BIS) during anesthesia, there have been contradictory reports regarding its effects. The purpose of this study was to investigate whether a muscle relaxant affected the level of BIS during propofol anesthesia. METHODS: Forty-eight healthy patients undergoing elective surgery under general anesthesia were enrolled in this prospective, randomized, double-blind study. All patients received an effect-site targeted concentration of propofol via a TCI system that was titrated until loss of consciousness occurred. The patients then received either an injection of vecuronium (relaxant group, n = 24) or normal saline as a placebo (placebo group, n = 24) at 3 minutes after loss of consciousness. The BIS and electromyogram (EMG) activity were recorded from anesthetic induction to 4 minutes after injection of the vecuronium or placebo. RESULTS: The BIS significantly decreased after injection in both groups (P < 0.05), however, the decrease in the BIS was larger in the relaxant group than in the placebo group (P < 0.05). The decrease of EMG activity was not significantly different between the two groups after administration of vecuronium or placebo. CONCLUSIONS: During propofol induction of anesthesia, a muscle relaxant decreased BIS significantly without decreasing the EMG activity.