NEUROMUSCULAR EFFECTS OF ROCURONIUM ON THE DIAPHRAGM AND ADDUCTOR POLLICIS MUSCLES IN ANESTHETIZED PATIENTS

Background: Rocuronium has properties that may make it suitable for rapid-sequence intubation. However, its neuromuscular effects have been studied only on the adductor pollicis. This study compares the neuromuscular effect of rocuronium on the diaphragm and adductor pollicis in humans. Methods: The forces generated by the diaphragm and the adductor pollicis during supramaximal single-twitch stimulation of the phrenic and ulnar nerves, respectively, were studied during thiopental, fentanyl, and nitrous oxide-oxygen anesthesia. In 6 patients, cumulative doses of 0.15, 0.25, 0.35, 0.45, and 0.60 mg.kg(-1) rocuronium were given over a 9-min period. The doses for 50% (ED(50)) and 95% (ED(95)) depression of twitch height were calculated. In another 12 patients, the times for maximal effect and 10%, 25%, 50%, 75%, and 90% recovery of the twitch height were calculated after a bolus dose of 0.60 mg.kg(-1) rocuronium. Results: ED(50) and ED(95) were higher for the diaphragm (0.26 +/- 0.07 and 0.50 +/- 0.20 mg.kg(-1), respectively) than for the adductor pollicis (0.14 +/- 0.05 and 0.24 +/- 0.04 mg.kg(-1)). Rocuronium 0.60 mg.kg(-1) produced 100% paralysis of the adductor pollicis in all patients and of the diaphragm in 9 of 12 patients. The onset time for muscle relaxation after 0.6 mg.kg(-1) rocuronium was shorter for the adductor pollicis than for the diaphragm (80 +/- 20 vs. 120 +/- 62 s). Times for 10%, 25%, 75%, and 90% recovery of twitch height were 34 +/- 10, 40 +/- 13, 56 +/- 20, and 64 +/- 21 min, respectively, for the adductor pollicis, and significantly shorter for the diaphragm: 17 +/- 10, 23 +/- 9, 33 +/- 13, and 35 +/- 10 min, respectively. Conclusions: The diaphragm is more resistant than the adductor pollicis to rocuronium, as shown by greater ED(50) and ED(95) and faster recovery of the twitch height. The intubating dose of 0.60 mg.kg(-1) is close to the ED(95), of 0.50 mg.kg(-1) for the diaphragm.