A comparison of midazolam and diazepam for induction of anaesthesia in high-risk patients

Fifty ASA Class III patients were divided randomly into two equal groups for induction of anaesthesia with diazepam 0.25 mg/kg, or midazolam 0.15 mg/kg. All subjects were premedicated with a narcotic and monitored by ECG, radial arterial catheter and a spirometer for measurement of minute ventilation. The QF interval (time period from the Q wave of the ECG to the foot of the radial artery pulse), mean arterial pressure, heart rate and minute ventilation were recorded before, during and immediately after the induction of anaesthesia. Although mean arterial pressure fell slightly (6%) following midazolam, all other cardiovascular variables were stable in both groups. Minute ventilation was depressed to 70% of control by both drugs and nearly one-half the diazepam patients complained of pain on injection compared with only one midazolam patient. These data suggest that midazolam is a reasonable alternative to diazepam for induction of anaesthesia in the high-risk patient.