Variability of onset times within and among relaxant regimens

Abstract

Study Objective: To evaluate the consistency of times to 95% twitch height depression (T 95%) in groups of patients receiving identical induction and relaxant regimens. Design: Prospective, noncontrolled, blinded study. Setting: Ambulatory sifgical unit at a university medical center. Patients: Seventy-five ASA physical status I and II patients undergoing general endotracheal anesthesia. Interventions: Patients received succinylcholine 1.5 m.g/kg or a nondepolarizing regimen with doses ranging from approximately 1.5 to 6 times the ED 95, with or without a priming dose. Measurements and Main Results: For each of the eight relaxant regimens used in five or more patients, the intraregimen variability of T 95% (at the adductor pollicis muscle upon ulnas stimulation at 0.1 Hz) was expressed as SD and range, and the individual data points were displayed. There was wide intraregimen variability. For each. regimen, the slowest T 95% was at least 73% longer than the fastest T 95% For the 16 patients receiving a priming dose plus an intubating dose 5 or more tunes the ED 95 the median T 95% was 95 seconds; however, T 95%, was beyond 120 seconds in 5 of tire 16 cases. Conclusions: The wide variability in onset times among subjects receiving the souse regimen indicates that monitoring of neuromuscular response, preferably to a relatively slow rate of neurostimulation, is essential q 'one elects to use moderate to high doses of atracurium and/or vecuronium,for rapid-sequence induction in a patient in wham movement or coughing is unacceptable. Since onset times were not symmetrical about the mean, the magnitude and frequency of unacceptable onset times would not be fully appreciated unless the individual data points were displayed. Such information may be critical when, reporting the suitability of a neuromuscular blocking drug for rapid intubation.