No abstract

No abstract

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. The effects of suxamethonium and tubocurarine on neuromuscular transmission in man were once regarded as simple. The block produced by tubocurarine was non-depolarizing and characterized by the presence of: (1) fade; (2) post-tetanic potentiation (facilitation); and (3) antagonism by cholinesterase inhibitors (Churchill-Davidson and Christie, 1959). The block initially produced by suxamethonium was depolarizing and was characterized by the absence of: (1) fade; (2) post-tetanic potentiation; and (3) antagonism by cholinesterase inhibitors (Churchill-Davidson and Christie, 1959). With sufficient dosage and the passage of time the suxamethonium block came to resemble the tubocurarine block and was labelled desensitizing (dual, mixed, phase II non-depolarizing) (Churchill-Davidson, Christie and Wise, 1960; Katz, Wolf and Papper, 1963). The present status is much more confusing. It has been suggested that after the first small dose of suxamethonium there is fade and post-tetanic