Onset of neuromuscular block at the masseter and adductor pollicis musclesfollowing rocuronium or succinylcholine

Purpose: To compare the onset time of two different rocuronium doses (0.6 a nd 0.9 mg kg(B1)) and succinylcholine (1.5 mg.kg(-1), preceeded by 0.06 mg. kg(-1) rocuronium) at the masseter and the adductor pollicis muscle. Methods: In a randomized study, 60 ASA I or II adult women, 18-65 yr of age . were anesthetized with propofol and fentanyl and nitrous oxide in oxygen. Neuromuscular monitoring was performed using acceleromyography simultaneou sly on the masseter and adductor pollicis. Onset time was measured at both muscles using supramaximal 0.1 Hz single twitch stimulation (square-wave pu lse 0.2 msec duration). Results: In all patients, complete neuromuscular block occured at the masse ter and adductor pollicis muscles. Lag-time and onset time were faster at t he masseter that at the adductor pollicis muscle in both rocuronium-groups (P < 0.01) and in the succinylcholine-group (P < 0.01). Furthermore, onset time was more rapid after 0.9 mg.kg(-1) rocuronium (65 +/- 7 s) than after succinylcholine (83 +/- 19 sec) at the AP (P < 0.05), but did not differ at the masseter(33 +/- 6 vs 36 +/- 7 sec). Conclusions: Following rocuronium and succinylcholine, onset time is faster at the masseter than at the adductor pollicis muscle.