Ephedrine shortens the onset of action of rocuronium but not of atracurium

HYPOTHESIS: Ephedrine increases blood flow to muscles and may shorten the onset of action of rocuronium and atracurium. MATERIAL AND METHODS: A prospective study of 80 ASA I-III patients undergoing surgery under general anesthesia and randomized to 4 groups: ephedrine-rocuronium, placebo-rocuronium, ephedrine-atracurium and placebo-atracurium. Atracurium or rocuronium was administered at a dose of 0.04 mg.Kg-1. We monitored neuromuscular function by acceleromyography, ECG and pulse oxymetry, arterial blood pressure (ABP) using an intra-arterial catheter (AT), heart rate (HR) and carbon dioxide pressure. Patient characteristics, time to onset, duration and recovery from the neuromuscular block were recorded. HR and ABP were measured at baseline, 3 minutes after ephedrine dosing, 1 minute after induction, immediately after intubation and 5, 10 and 20 minutes after intubation. RESULTS: Patient characteristics were similar in all groups. The time to onset of neuromuscular block was significantly shorter in the rocuronium and rocuronium-ephedrine groups than in the atracurium groups. Duration and recovery were similar in all groups. Patients premedicated with ephedrine experienced a significant increase in HR for 20 minutes. The only complications were 2 cases of self-limiting sinus tachycardia of less than 130 beats.min-1 in the ephedrine group. CONCLUSIONS: Premeditation with 10 mg of ephedrine decreases the time until onset of action of rocuronium but does not affect the timing of atracurium.