The Bispectral Index During Induction of Anesthesia with Midazolam and Propofol

This study evaluated the bispectral index as an indicator of anesthetic depth in relation to the cardiovascular response to intubation. Two treatments were compared: group 1 (n = 8) received propofol for induction of anesthesia (2 mg/kg bolus followed by an infusion of 0.20 mg/kg-1/min-1, group 2 (n = 8) was given 90 micrograms/kg midazolam 2 min before, followed by anesthesia with half-strength propofol (1 mg/kg bolus with infusion of 0.10 mg/kg-1/min-1). The bispectral index of the electroencephalogram, blood pressure, and heart rate were measured under unanesthetized conditions, during anesthetic induction, intubation, and a 15-min period after intubation. The duration of anesthesia and the total propofol requirement were recorded. Midazolam pretreatment produced transient decreases in blood pressure and the bispectral index. During anesthetic induction with propofol, blood pressure decreased 20% in both groups, and the bispectral index decreased to lower levels in group 1 (29 +/- 9) than in group 2 (47 +/- 22). Intubation increased blood pressure more in group 2 (50 +/- 10 mm Hg) than in group 1 (30 +/- 12 mm Hg). Throughout the rest of the surgery, more propofol was used in group 1 (77 +/- 14 micrograms/kg-1/min-1) than in group 2 (42 +/- 14 micrograms/kg-1/min-1). These results show that the decrease in bispectral index provides an indication of the blood pressure increase to intubation during propofol anesthesia. Midazolam pretreatment did not attenuate the cardiovascular response to intubation but did decrease propofol use during surgery.