BACKGROUND: Rocuronium may replace succinylcholine for intubation in general endotracheal anesthesia. However, intravenous bolus injection of rocuronium produces the responses of pain and withdrawal. We hypothesized that the infusion of rocuronium during endotracheal intubation could decrease these responses without influencing the intubating condition.

METHODS: One hundred and twenty patients were randomly assigned to one of four groups (B2, I2, B3, and I3), divided by the injection methods (B2 and B3: bolus injection, I2 and I3: infusion injection for 60 sec) and doses of rocuronium (B2 and I2: 0.6 mg/kg, B3 and I3: 0.9 mg/kg). After loss of consciousness with thiopental sodium (5 mg/kg), rocuronium was injected intravenously as arranged in every groups. Withdrawal response to rocursonium injection was assessed by 4-grade scale (score 0-3). Muscle relaxation was monitored by fade out time of single twitch stimulation, and the intubating condition was assessed by the total score of 4-grade scales (score 0-3) of jaw relaxation, vocal cord opening and response to intubation.

RESULTS: The withdrawal scores of the infusion groups (I2 and I3) were lower than those of the bolus groups (B2 and B3) (P < 0.05). The fade out time of single twitch stimulation was shorter in large dose (0.9 mg/kg) of rocuronium (P < 0.05), but it was not different regardless of injection methods (bolus vs. infusion). Intubating condition was also better in large dose group than small dose regardless of their injection methods.

CONCLUSIONS: The infusion of rocuronium for endotracheal intubation effectively reduces the withdrawal response compared with bolus injection, and it neither delays the onset of muscle relaxation nor deteriorates the intubating condition during endotracheal intubation.