ROCURONIUM PRIMING OF ATRACURIUM-INDUCED NEUROMUSCULAR BLOCKADE - THEUSE OF SHORT PRIMING INTERVALS

Study Objective: To evaluate the effects of priming doses of rocuroniu m on the duration of priming interval and on the outcome of priming se quence using rocuronium-atracurium combination. Design: Three phase, r andomized, controlled study. Setting: Inpatient anesthesia in a univer sity hospital. Patients: 144 ASA physical status I and II patients, 19 to 57 years of age, weighing 50 to 90 kg, and undergoing low-risk ele ctive surgery. Interventions: Phase I, two equal groups (n = 12) of ad ult patients anesthetized with propofol, fentanyl, and nitrous oxide ( N2O), received a priming dose of rocuronium 0.1 mg/kg or vecuronium 0. 015 mg/kg. Phase II included six equal groups (n = 12): Groups 1, 2, a nd 3 received a priming dose of rocuronium 0.1 mg/kg and atracurium 0. 42 mg/kg for intubation. The priming intervals were, respectively, 1, 1.5, or 2 minutes in Groups 1, 2, and 3. Groups 4, 5, and 6 received, respectively, a bolus dose of rocuronium 0.6 mg/kg, atracurium 0.5 mg/ kg, or succinylcholine 1 mg/kg. Intubation was performed at maximum bl ock. Phase III included four equal groups (n = 12). A priming dose of rocuronium 0.1 mg/kg (Group 1) or a placebo (Groups 2, 3, and 4) was g iven to awake patients. Anesthesia was induced during the one-minute p riming interval. Intubating doses of atracurium 0.42 mg/kg, rocuronium 0.6 mg/kg, atracurium 0.5 mg/kg, or succinylcholine 1 mg/kg were give n to Groups 1, 2, 3, and 4, respectively. Intubation was attempted 1 m inute after intubating doses were administered. Measurements and Main Results: Adductor pollicis responses to train-of-four stimulation was recorded mechanically in Phases I and II only. The priming interval af ter rocuronium 0.1 mg/kg was in the range of 1 to 2 minutes. Priming d oses of rocuronium resulted in significant acceleration in the onset t ime of intubating doses of atracurium, irrespective of the duration of the priming interval. The onset times [mean (SD)] following rocuroniu m-atracurium sequence in Groups 1, 2, and 3 were, respectively, 67 (17 ), 73 (14), and 66 (18) seconds and were comparable with the onset of bolus doses of rocuronium and succinylcholine. In Phase II, good to ex cellent intubating conditions were obtained in 41% to 58% of patients included in Groups 1 through 5. Excellent to good intubating condition s were obtained in all patients (100%) who received succinylcholine. I n Phase III, good to excellent intubating conditions were obtained in 91% of patients who received rocuronium-atracurium sequence. Symptoms of muscle weakness were not reported. Conclusions: Priming doses of ro curonium 0.1 mg/kg reduce the priming interval to 1 minute, allow earl y induction of anesthesia, eliminate patient discomfort, and accelerat e the onset time of atracurium with intubating conditions comparable w ith succinylcholine and rocuronium.