The pharmacodynamics of rocuronium in pediatric patients anesthetized with halothane

The aim of this study was to determine the neuromuscular blocking potency of rocuronium (ORG 9426) in 4-to 14-year old children anesthetized with halothane. After induction of anesthesia, the ulnar nerve was stimulated with electrical impulses of 0.2 ms duration every 12 s and the force of contraction of the thumb (P) was continuously recorded. Doses of 0.12, 0.16, 0.20, and 0.24 mg·kg(-1) rocuronium were administered, in a randomized fashion, to 4 groups of 12 patients each. The ED50, ED90, and ED95 of rocuronium determined from the log dose-probit regression lines were 0.18, 0.34, and 0.40 mg·kg(-1), respectively. To facilitate tracheal intubation, after the development of the maximal effect of the first dose, a variable second dose of rocuronium was administered to increase the total dose to 0.3 mg·kg(-1). If after the second dose P was greater than 10% of control, additional 0.025-0.1 mg·kg(-1) increments of rocuronium were administered until P became less than 10% of control. At this time the trachea was intubated. Muscular relaxation was maintained with 0.075, 0.1, or 0.125 mg·kg(-1) rocuronium, administered whenever P recovered to 25% of control. The clinical duration of these doses was 6.9±2.8, 6.1±0.4, and 8.1±0.6 min, respectively. On repeated administration of three 0.1 or 0.125 mg·kg(-1) doses, rocuronium showed little cumulative tendency. Time for spontaneous recovery of P from 25% to 75%, 8.4±0.39 min and from 10% to 90%, 16.19±0.15 min, of control, were relatively short. When at termination of anesthesia T4/T1 ratios were lower than 0.75, the residual neuromuscular block could be antagonized with 0.5 mg·kg(-1) edrophonium in 2 min. Rocuronium, 0.3 mg·kg(-1) caused a 13.5% increase of heart rate but had no effect on blood pressure. In conclusion, in 4 to 14-year-old children, rocuronium appears to have a more rapid onset and shorter duration of action than other steroid-type muscle relaxants.