Electromyographic and mechanical effects of suxamethonium and tubocurarine on twitch, tetanic and post-tetanic responses.

In an effort to reconcile conflicting reports in the literature concerning suxamethonium and tubocurarine, we studied the effects of these agents on the adductor pollicis mechanical twitch, adductor pollicis brevis compound action potential and abductor digiti quinti compound action potential. It was observed that the magnitude of block of the adductor pollicis differed from that of the abductor digiti quinti. In addition the magnitude of adductor pollicis block recorded mechanically differed from that recorded electrically. It was further observed that the presence or absence and magnitude of fade and post-tetanic potentiation depended upon the muscle studied, the rate of stimulation, the anaesthetic technique employed, the degree of block and whether electrical or mechanical responses were recorded. Nevertheless, by recording electrical and mechanical effects, it was possible to distinguish clearly the depolarizing block produced by suxamethonium from the desensitizing block produced by this agent as well as from the non-depolarizing block produced by tubocurarine.