Comparison of the efficacy of chlormethiazole and diazepam as i.v. sedatives for supplementation of extradural anaesthesia.

The clinical efficacy of two sedative agents was compared in 21 young healthy patients undergoing surgery under extradural blockade. A state of sedation and amnesia in which patients lapsed into a sleep-like state when left undisturbed, yet spontaneously opened their eyes to make comments and co-operate with verbal commands, was sought. This was achieved readily by careful titration of responses and required a diazepam loading dose of 20 (+/- 15) mg given at a rate of 1 mg min-1 or 0.8% chlormethiazole edisylate infusion 10 ml min-1 given over 16 (+/- 6) min. Control of this state was easier with chlormethiazole (by varying the rate of infusion) than by giving repeated doses of diazepam. Both agents provided good anterograde amnesia; there was no retrograde amnesia. Considerable postoperative somnolence with a high incidence of relapse into amnesic and sedated states were noted with both agents. However, if the total volume of chlormethiazole infused was less than 300 ml, then a distinct advantage of abrupt and lucid recovery was apparent. Blood concentrations producing the desired clinical state were more variable for diazepam than for chlormethiazole.