Canadian Journal of Anesthesia, Vol 43, 1134-1137, Copyright © 1996 by Canadian Anesthesiologists' Society

ARTICLES

Optimal dose of thiamylal in combination with midazolam for induction of anaesthesia

T Nishiyama and K Hanaoka
Department of Anesthesiology, Faculty of Medicine, University of Tokyo, Japan.

PURPOSE: The optimal dose range of thiamylal, combined with midazolam, in the induction of anaesthesia was evaluated using haemodynamic variables. METHODS: The 200 patients, aged 30 to 70 yr, were randomly divided into five groups by midazolam dosage. Anaesthesia was induced with midazolam 0.05, 0.075, 0.10, 0.15, or 0.20 mg.kg-1. Two minutes later, 50 mg thiamylal was administered followed by 25 mg increments until verbal response and eyelash reflex disappeared and blood pressure decreased to a level less than that of preinduction. Tracheal intubation was performed with 0.15 mg.kg-1 vecuronium. Blood pressure and heart rate were monitored during induction. Optimal induction was defined as a systolic blood pressure one minute after intubation within +/- 20% of that before induction. RESULTS: There were 164 patients whose systolic blood pressure were within these criteria. Blood pressure decreased two minutes after induction and 3 to 15 min after intubation in all groups. Heart rate increased one minute after intubation in 0.05 mg.kg-1, 0.075 mg.kg-1 and 0.10 mg.kg-1 midazolam groups. The optimal range of thiamylal was 4.0 +/- 1.1 (mean + SD), 3.1 +/- 1.2, 2.8 +/- 1.1, 2.3 +/- 1.2, and 1.7 +/- 1.0 mg.kg-1 in combination with midazolam 0.05, 0.075, 0.10, 0.15, and 0.20 mg.kg-1, respectively. CONCLUSION: The optimal dose range, to maintain haemodynamic stability, for thiamylal induction of anaesthesia in combination with midazolam, 0.05-0.2 mg.kg-1 was found to range from 4.0 to 1.7 mg.kg-1.