: Neuromuscular transmission was studied in anesthetized patients during intra-arterial infusion of succinylcholine. Phase I and Phase II block were demonstrated in man during continuous succinylcholine infusion at various concentrations. During Phase II block, as identified by non-sustained tetanus and post-tetanic facilitation, anticholinesterases (e.g., edrophonium and neostigmine injected intravenously) produced either a slight transient reversal of block or no effect at all during the period of infusion. Recovery of neuromuscular transmission after succinylcholine infusion was rapid and complete unless neostigmine had been used in large doses. Recovery after large doses of neostigmine was markedly prolonged.
It is proposed that the terms "Phase I" and "Phase II" or alternately "Dual Block" be discontinued. Instead it is proposed to label the early period of decreased tension output as "Depolarization Block"; the later period of decreased neuromuscular transmission as "Desensitization Block." Both types of block begin at the moment of application of depolarizing drugs but they are due to different mechanisms which become apparent with time. These suggested discriptions are more consistent with the observed experimental data than are the customary terms.
(C) 1966 American Society of Anesthesiologists, Inc.