Rapid sequence induction (RSI) is indicated in various situations. Succinylcholine has been the muscle relaxant of choice for RSI, and rocuronium has become an alternative medicine for patients who cannot be administered succinylcholine for various reasons. Although rocuronium has the most rapid onset time among non-depolarizing muscle relaxants, the standard dose of rocuronium (0.6 mg/kg) takes 60 seconds to achieve appropriate muscle relaxation. We evaluated intubating conditions using the "modified timing principle" with rocuronium and succinylcholine.

In this prospective controlled blinded study, all patients received 1.5 µg/kg fentanyl intravenously with preoxygenation for 2 minutes and were randomized to receive 0.6 mg/kg rocuronium followed by 1.5 mg/kg propofol or 1.5 mg/kg propofol and 1.5 mg/kg succinylcholine. The rocuronium group was intubated just after confirming loss of consciousness, and the succinylcholine group was intubated 1 minute after injecting succinylcholine. Intubation condition, timing of events, and complications were recorded.

All patients were successfully intubated in both groups. Apnea time of the rocuronium group (38.5 seconds) was significantly shorter than that in the succinylcholine group (100.7 seconds). No significant differences were observed in loss of consciousness time or intubation time. The succinylcholine group tended to show better intubation conditions, but no significant difference was observed. None of the patients complained awareness of the intubation procedure or had respiratory difficulty during a postoperative interview.

The modified RSI with rocuronium showed shorter intubation sequence, acceptable intubation conditions, and a similar level of complications compared to those of conventional RSI with succinylcholine.