The effect of d-tubocurarine priming on an ED 95 dose of vecuronium bromide

Abstract

Study Objective: To examine how priming with ED 10 d-tubocurarine prior to the administration of ED 95 vecuronium bromide affects onset and duration of neuromuscular blockade. Design: Prospective, randomized, observer-blinded study. Setting: Operating room at a university cancer center. Patients: 40 ASA physical status I and II patients undergoing ambulatory surgical procedures. Interventions: Patients were randomized to one of two groups. Group 1 patients received d-tubocurarine 50 μg/kg intravenously (IV), followed by vecuronium 60 μg/kg IV. Group 2 patients received vecuronium 60 μg/kg IV without priming. All patients received a total IV anesthetic consisting of alfentanil and propofol for induction of anesthesia and propofol alone for maintenance of anesthesia. Measurements and Main Results: Onset of muscle relaxation was determined with an electromyograph (Datex Relaxograph), documenting time to 80% depression of the first twitch in a train-of-four (T 180%), percent depression of T 1 at 60 and 90 seconds (T 160 and T 190, respectively), T 4:T 1 ratio at 90 seconds, and time to achieve maximal blockade (B max). Recovery was evaluated by measuring the time required for return of T 1 to 25% of the baseline value. Intubating conditions were assessed at 90 seconds after vecuronium administration and graded on a 1 (jaw tight, impossible to intubate) to 4 (jaw relaxed, vocal cords immobile) scale. All criteria measuring onset of neuromuscular blockade ( i.e., T 180%, T 160, T 190, T 4:T 1, and B max) were significantly shorter ( p < 0.05) in patients who received d-tubocurarine. Recovery was similar in both groups. Intubation scores were significantly better 90 seconds after priming ( p < 0.05). Conclusions: These results indicate that crossover dosing of nondepolarizing muscle relaxants may have synergistic effects. Priming with ED 10 d-tubocurarine prior to an ED 95 dose of vecuronium shortens the time to 80% T 1 depression and produces satisfactory intubating conditions at 90 seconds, without prolonging the duration of the block. Therefore, d-tubocurarine is an attractive drug for priming vecuronium in short operative procedures that require muscle relaxation.