Time interval between alfentanil and rocuronium administration necessary to prevent rocuronium-induced withdrawal movement

Background: We aimed to determine the time interval between alfentanil and rocuronium administration, at a 50% probability of preventing pain-induced withdrawal movement from rocuronium injection (Time(AR)50). Methods: A total of 64 patients scheduled for general anesthesia were enrolled in this study (33 men and 31 women). Anesthesia was induced with target-controlled infusion of propofol, at an effect-site target concentration of 3 mu g/mL. Then, alfentanil 15 mu g/kg was injected for 30s. After 60s, rocuronium 0.6 mg/kg was administered to the first patient. The Dixon's up-and-down method was used to determine the time interval for each subsequent patient (interval of 5 s). Mean arterial pressure (MAP) and heart rate (HR) were recorded at three time points: T0, pre-induction; T1, before rocuronium injection; and T2, 1 min after rocuronium injection. Results: The Time(AR)50 +/- standard deviation (SD) was 5.6 +/- 3.7 s and 21.9 +/- 5.6s in the male and female patients, respectively. Based on the probit regression, the Time(AR)50 was 4.7s (95% confidence interval [CI], 1.2-7.6s) and 20.3s (95% CI, 7.7-26.1 s) in the male and female patients, respectively. The Time(AR)95 was 10.6s (95% CI, 7.7-25.3s) and 35.0s (95% CI, 28.1-95.5s) in the male and female patients, respectively, with significantly higher values in females than in males (P<0.001). Compared with the T0, MAP and HR decreased significantly at T1 and T2 in both groups. Conclusion: The Time(AR)50 required for preventing rocuronium-induced withdrawal movement were 4.7s and 20.3s in male and female patients, respectively.