Effects of propofol and midazolam on bispectral index

Objective To compare the effects of midazolam and propofol on bispectral index (BIS). Methods Sixty elective unpremedicated outpatients without history of having any hypnotic and sedatives or psychiatric diseases were randomly allocated to two groups with 30 cases each receiving either midazolam or propofol for induction. With sequential experimental method, a series doses of midazolam or propofol were used for observation of loss of consciousness and changes in BIS. The loss of responses to verbal command and eyelash stimulation was used as a standard identifying unconsciousness while recording BIS. The data were analyzed with linear regression and calculated with weighted averaging for obtaining BIS50 and ED50.Results With midazolam induction, there was a marked fall in BIS compared with the control value, but there was no significant difference between sleepers and non-sleepers. The values of BIS50 and ED50 for midazolam were 77.02 (95% confidence interval of 71.08-85.86) and 0.1237 mg/kg (0.0990-0.1540 mg/kg) respectively. With propofol induction, there was little fall in BIS in non-sleepers, but a marked fall in sleepers, showing a significant difference between them. The values of BIS50 and ED50 for propofol were 79.17 (72.08-88.55) and 1.0192 mg/kg (0.9400-1.1480 mg/kg) respectively.Conclusion Midazolam and propofol have different effect on BIS. BIS value is less associated with hypnotic effect of midazolam than with that of propofol.