Midazolam for induction of anaesthesia in outpatients: a comparison with thiopentone.

Midazolam, a new water-soluble benzodiazepine, with an elimination half-life of approximately 2 h, was compared with thiopentone for induction of general anaesthesia in a randomized, single-blind study. The patients were 60 healthy women undergoing legal abortion as outpatients. Midazolam provided smooth and reliable induction of anaesthesia with few side-effects. However, the induction time was considerably longer in the midazolam group (82.3 + 6.1) than in the thiopentone group (45.9 +/- 1.7s). The dose of midazolam required for induction was 0.36 +/- 0.01 mg/kg, while that of thiopentone was 6.43 +/- 0.21 mg/kg. Apnoea occurred with a frequency of 10% in the midazolam group and 55% in he thiopentone group, but was of equal duration in both groups. Circulatory conditions were more stable during induction with midazolam, with a slower fall in blood pressure and no change in heart rate. The patient were breathing O2/N2O in proportions of 1:2. To ensure adequate surgical anaesthesia, it was necessary to add halothane for short periods for all patients in the midazolam group and for 79% of the thiopentone group. Postoperatively, all patients who had received midazolam, but none induced with thiopentone, had anterograde amnesia; this lasted for more than 1 h. All patients in both groups could leave the hospital after routine postoperative observation for 3-4 h. Venous tolerance was good for both drugs.