THE CLINICAL NEUROMUSCULAR PHARMACOLOGY OF CISATRACURIUM VERSUS VECURONIUM DURING OUTPATIENT ANESTHESIA

Neither comparisons of the clinical neuromuscular effects of cisatracu rium and vecuronium nor comparative studies of their antagonism by neo stigmine have been reported. In addition, the efficacy of administerin g cisatracurium in divided doses has not been investigated. Accordingl y, we applied supramaximal electrical stimuli to the ulnar nerve of 16 5 ASA physical status I and II patients receiving nitrous oxide/alfent anil/propofol anesthesia. Forty-five patients received cisatracurium 5 , 10, or 15 mu g/kg, and the evoked response at the adductor pollicis was recorded for 15 min. One hundred-twenty patients received cisatrac urium 5, 10, or 15 mu g/kg or normal saline placebo followed 5 min lat er by either cisatracurium 100 mu g/kg or vecuronium 100 mu g/kg (alwa ys after placebo). Time to clinical onset (maximal ablation of single twitch response) was measured. When the evoked response spontaneously recovered to 10% of control height, neostigmine 5, 10, 30, or 50 mu g/ kg or placebo was administered, and recovery of neuromuscular function was recorded for the next 15 min. The clinical onset of vecuronium wi thout priming (2.8 +/- 0.8 min) (mean +/- SD) was significantly (P < 0 .05) faster than the onset of cisatracurium without priming (4.6 +/- 1 .4 min). Cisatracurium 5, 10, or 15 mu g/kg administered before cisatr acurium 100 mu g/kg significantly (P < 0.05) accelerated the time to c omplete ablation of the evoked response (3.9 +/- 0.9, 2.9 +/- 0.8, or 3.0 +/- 0.9 min, respectively) compared with cisatracurium 100 mu g/kg without priming. The dose of neostigmine required to achieve 50% assi sted recovery of the train-of-four ratio at 5 min was significantly (P < 0.05) smaller in patients who received vecuronium (29.1 [17.9-55.3] mu g/kg) (mean [95% confidence interval]) compared with those who rec eived cisatracurium (53.7 [31.6-131.5] mu g/kg). Given its faster clin ical onset and greater sensitivity to antagonism by neostigmine, we co nclude that vecuronium may be more suitable than cisatracurium for use in outpatient anesthesia. Implications: We investigated the onset of muscle relaxation using intravenous vecuronium and cisatracurium and a ssessed the ability of neostigmine to antagonize (reverse) this effect . Our results suggest that vecuronium works faster than cisatracurium and is more sensitive to neostigmine. Vecuronium therefore may be more useful than cisatracurium in outpatient anesthesia.