ONSET AND DURATION OF ROCURONIUM AND SUCCINYLCHOLINE AT THE ADDUCTOR POLLICIS AND LARYNGEAL ADDUCTOR MUSCLES IN ANESTHETIZED HUMANS

Background: Rocuronium, a new nondepolarizing muscle relaxant, has a r apid onset of activity and may be suitable as a component of a rapid-s equence induction of anesthesia. We evaluated a range of doses on onse t and duration of effect at the larynx and the adductor pollicis and c ompared these characteristics with those of succinylcholine. Methods: Forty-eight patients aged 18-70 yr, of ASA physical status 1-3, were r andomly allocated to receive succinylcholine (1 mg/kg) or one of three doses of rocuronium (0.4, 0.8, or 1.2 mg/kg) during surgery. Anesthes ia was induced and maintained with propofol and fentanyl. The trachea was intubated without the use of muscle relaxants, and the cuff of the endotracheal tube placed between the Focal cords. Neuromuscular trans mission was monitored by mechanomyography at the laryngeal adductor an d adductor pollicis muscles. Muscular activity was evoked with suprama ximal stimuli in a train-of-four sequence every 12 s to the anterior b ranch of the recurrent laryngeal nerve and the ulnar nerve. Results: A t the laryngeal adductors, peak effect exceeded 99% in all patients gi ven succinylcholine and in none (0%), five (42%), and ten (83%) of tho se given rocuronium 0.4, 0.8, and 1.2 mg/kg, respectively. At the addu ctor pollicis, peak effect exceeded 93% in all study patients except t wo who received rocuronium 0.4 mg/kg (peak effects 91% and 97%). Onset of effect with succinylcholine was significantly more rapid at the la ryngeal adductors (34 +/- 12 s, mean +/- SD) than at the adductor poll icis (56 +/- 15 s); this was true also for rocuronium 0.4 mg/kg (92 +/ - 29 s and 155 +/- 40 s for the laryngeal adductors and adductor polli cis, respectively). Onset times were similar at the two muscle groups with rocuronium 0.8 and 1.2 mg kg(-1): 36 +/- 29 and 74 +/- 36 s with 0.8 mg/kg and 54 +/- 30 and 65 +/- 21 s with 1.2 mg/kg at the laryngea l adductors and the adductor pollicis, respectively. Conclusions: The laryngeal adductors are more resistant to the action of rocuronium tha n is the adductor pollicis. Consequently, the onset of effect of rocur onium, in doses greater than 0.8 mg/kg, is similar to that of succinyl choline at the adductor pollicis but is significantly delayed compared with that of succinylcholine at the laryngeal adductors.