• G A Turner, J D Williams, and D J Baker.
• Department of Anaesthetics, Royal Naval Hospital, Haslar, Gosport Hampshire.
• Br J Anaesth. 1989 Mar 1;62(3):279-86.

AbstractThe actions of alcuronium, vecuronium and tubocurarine have been studied in the isolated forearms of six healthy, non-anaesthetized volunteers. The responses of adductor pollicis were measured during onset and recovery of neuromuscular block for each agent. There was a drug-related disparity between mechanomyogram (MMG) and electromyogram (EMG) measurement of the first response of the train-of-four (T1) and of the ratio of the fourth (T4) to the first response (TOF ratio). There were significantly higher T1 values for the EMG than for MMG during alcuronium blockade (P = 0.03). For tubocurarine, however, the relationship was reversed. The relationship between T1 and TOF ratio during onset and recovery of neuromuscular block was a hysteresis. The TOF ratio at 50% T1 was significantly higher during onset than during recovery for all three drugs, measured by MMG or EMG (P less than 0.005). Analysis of variance of the differential fade loops failed to show a drug-related effect. We conclude that care should be taken in assuming interchangeability between MMG and EMG measurement of T1. Relationships between T1 and TOF ratio derived during recovery do not necessarily apply during onset and may lead to error in estimating the degree of muscle relaxation.

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