Dose-related effects of succinylcholine on the adductor pollicis and masséter muscles in children

This study was performed to détérmine the effects of various doses of succinylcholine on resting tension and evoked twitch height at the masséter and adductor pollicis muscles in children. Twenty patients, aged 3-10yr, ASA physical status I or II, were randomly assigned to receive succinylcholine 0.15, 0.25, 0.50 or 1.00 mg · kg^-1, during halothane-nitrous oxide anaesthesia. Supramaximal train-of-four stimulation was applied simultaneously to the ulnar nerve and the nerve to the masséter. Transducers recorded force at the jaw and the thumb. Maximum blockade of the first twitch (T₁) and maximum resting tension change were measured. Potency of succinylcholine at the two muscles was estimated by linear regression of the logit transformation of T₁ versus log dose. The relationship between resting tension change and log dose was established by linear regression. The masséter muscle was more sensitive to succinylcholine than the adductor pollicis with an ED₉₅ of 0.28 ± 0.02 (mean ±SEM) vs 0.44 ± 0.05 mg · kg^-1 (P < 0.05). Onset of neuromuscular blockade was faster at the masséter, and recovery occurred simultaneously in both muscles. A dose-related increase in resting tension was observed in both muscles, but its magnitude was five times greater at the masséter. With succinylcholine, 1 mg · kg^-1, this increase was 51.6 ± 16.8 g at the masséter and 9.1 ± 2.3 g at the adductor pollicis. Tension returned to baseline within 1-2 min. It is concluded that in children (1) succinylcholine produces dose-related changes in resting tension; (2) this effect, although quantitatively important at the masséter, is not restricted to that muscle; and (3) relatively small doses of succinylcholine are required to block neuromuscular transmission at the jaw.