Median Effective Dose of Remifentanil for the Prevention of Pain Caused by the Injection of Rocuronium: An Age-Stratified Study

INTRODUCTION: Rocuronium intravenous pain is common in induction of general anesthesia. The aim of our study was to determine the median effective dose (ED(50)) of prophylactic intravenous remifentanil for the prevention of rocuronium injection pain and to explore the effect of age on the ED(50). METHODS: Eighty-nine adult patients undergoing elective general anesthesia, ASA I or II, regardless of gender or weight, were stratified according to age: group R1 18–44 years, group R2 45–59 years, and group R3 60–80 years. The initial dose of prophylactic remifentanil before rocuronium injection was set at 1 μg/kg lean body weight (LBW). The remifentanil doses were adjusted according to the degree of injection pain using the Dixon sequential method, with a ratio of 1.1 between adjacent doses. Injection pain was graded, and the occurrence of injection pain and adverse reactions were recorded. The ED(50) and 95% confidence intervals (CIs) of remifentanil were calculated using the Dixon–Massey formula. Patients were asked whether they recalled feeling any injection pain in the post-anesthesia care unit (PACU). RESULTS: The ED(50) (95% CIs) of prophylactic remifentanil for the prevention of rocuronium injection pain were 1.266 μg/kg (1.186–1.351 μg/kg), 1.188 μg/kg (1.065–1.324 μg/kg), and 1.070 μg/kg (1.014–1.129 μg/kg) LBW in group R1, group R2, and group R3, respectively. No adverse reactions to remifentanil occurred in any group. In PACU, 84.6, 86.7, and 85.7% of patients who experienced injection pain had memories of the pain in group R1, group R2, and group R3, respectively. CONCLUSIONS: Prophylactic intravenous remifentanil can prevent rocuronium injection pain, and its ED(50) decreases with age, with 1.266 μg/kg (18–44 years), 1.188 μg/kg (45–59 years), and 1.070 μg/kg LBW (60–80 years), respectively. TRIAL REGISTRATION: ClinicalTrials.gov: NCT05217238 (registration date 18 Dec 2021).