Purpose: The present study was undertaken to evaluate onset, and early and late recovery of neuromuscular block after a combination of mivacurium (M) and rocuronium (R).
Methods: In this controlled, randomized study, 45 consenting ASA I-II patients were assigned to one of three treatment groups: 2.ED95 R alone (2R); 2.ED95 R plus 1.ED95 M (2R1M). or 2.ED95 R plus 2.ED95 M (2R2M). Neuromuscular monitoring of the ulnar nerve consisted of surface electrode stimulation and force transduction of the adductor pollicis muscle. Stable baseline stimulation (1 Hz, square-wave, supramaximal current) was established prior to relaxant administration and continued until 95 percent twitch height depression (onset). Thereafter, train-of-four stimulation every 10 seconds was used to record recovery data until 95 percent recovery (T(95%)). Data were analyzed using grouped t-tests, ANOVA, and Newman-Keuls multiple comparison tests. Significance was defined at the p < 0.05 level.
Results: The addition of mivacurium to rocuronium did not accelerate onset of block. The combination prolonged the clinical duration (time to 5 percent recovery, T(5%)), but did not affect subsequent recovery parameters: T(5%) in the 2R1M and 2R2M groups were 100 percent and 118 percent longer than in the 2R group, respectively (p < 0.05) the T(5-25%) (early recovery) and T(25-75%) (linear recovery) indexes were similar in all three groups.
Conclusions: The present study did not note an acceleration of block onset when mivacurium was added to rocuronium. The findings suggest that the addition of mivacurium (1-2.ED95) to rocuronium (2.ED95) prolongs the clinical duration of the longer-acting agent, rocuronium, but has no effect on the early or linear recovery indexes of rocuronium. Thus, although clinical duration is prolonged, recovery from the combination regimens proceeds as if no mivacurium had been added to rocuronium.