Characteristics of the Neuromuscular Block With Succinylcholine and Decamethonium in Man

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Abstract
Characteristics of the neuromuscular block produced by succinlcholine and by decamethonium were studied in 32 subjects anesthetized with halothane. Electromyograms (EMG) and tension of the adductor pollicis brevis muscle were recorded simultaneously. The neuromuscular block presented from the onset the typical characteristics of a phase II block: fade of EMG amplitude and fatigue of muscle tension during tetanization, as well as post-tetanic facilitation. Phase I neuromuscular block, characterized by constant tetanic responses of EMG and tension, and by absence of post-tetanic facilitation was never observed, even with smallest effective blocking doses of succinylcholine or de-camethonium. Fade of EMG and fatigue of tension increased proportionately with block; the more profound the block, the more pronounced the fade and fatigue. Whereas fade and fatigue increased progressively as more drug was given, post-tetanic facilitation was related neither to dosage nor to duration of administration of the drug. Thus facilitation was of little value in defining state of neuromuscular block during prolonged administration. The neuromuscular block produced by succinylcholine and decamethonium had from its onset the electromechanical characteristics of a phase II block. Hence phase I and phase II block cannot be differentiated on the basis of muscle response to nerve stimulation.