Twitch, Tetanus and Train-of-Four as Indices of Recovery from Nondepolarizing Neuromuscular Blockade

Abstract
The sensitivities of the train-of-4 response (2 Hz for 2 s), the single twitch (0.15 Hz) and the tetanic response (50 Hz for 5 s) were compared as indices of residual nondepolarizing block. Spontaneous or induced recovery of evoked thumb adduction in response to ulnar nerve stimulation was studied. Adult surgical patients (107) were divided according to the relaxant used [d-tubocuraraine, metocurine, pancuronium], into 6 groups. When the single twitch recovered to control height, the train-of-4 ratio was well below 1.0. This ratio was significantly lower during spontaneous recovery than following neostigmine antagonism of the block. The tetanic response was fully sustained when the train-of-4 ratio was > 0.7. When the ratio was < 0.7, variable degrees of fade of tetanus were evident. Analysis of variance indicated similar train-of-4 ratios among the 6 groups at complete recovery of the single twitch irrespective of the relaxant technique used. A train-of-4 ratio of 0.7 or higher reliably indicates the recovery of the single twitch to control height and a sustained response to tetanic stimulation at 50 Hz for 5 s. The clinical significance of this study is as follows: the train-of-4 response provides the same indication of clinical recovery from nondepolarizing block as obtained from tetanic stimulation at a physiological frequency; and reliance on the recovery of the single twitch to control height as a criterion of spontaneous return to normal clinical neuromuscular function may be misleading.

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