Artery-to-muscle onset time for neuromuscular blocking drugs

Artery-to-muscle (A-M) onset time for five neuromuscular blocking agents was studied in 50 female patients under light endotracheal anaesthesia. Circulation to the right arm was occluded by a tourniquet and released 1 min after the injection i.v. into the left arm of a myoneural blocking drug. Muscle twitches were recorded in the right hand after stimulation of the ulnar nerve (1 Hz). After releasing the tourniquet the response to single twitches continued without decrease in height (latent onset time). The onset of gradual decreases in twitch height was noted, and the time until 90% depression of twitch height was measured (manifest onset time). The mean latent onset times were: pancuronium 31.9 s, tubocuraine 21 s, alcuronium 17.2 s, fazadinium 8.6 s and suxamethonium 4.8 s. Mean A-M latent onset time was significantly different for each drug (P less than 0.005). Manifest A-M onset times were related to A-M latent onset time except for tubocurarine which exhibited a slower decline in twitch height. A-M latent onset time correlated well with the values for intravenous onset times reported in the literature.