Optimal remimazolam infusion rate for general anesthesia induction in elderly patients: a dose determination study by the <i>k</i>-in-a-row method

Elderly patients commonly experience sudden hypotension after propofol administration for anesthesia induction. Remimazolam, a novel anesthetic agent, offers superior hemodynamic stability, and thus represents a potentially safer alternative to propofol in this vulnerable population. However, the optimal infusion rate of remimazolam for inducing general anesthesia in elderly patients remains unclear. This study aimed to determine the effective infusion rate of remimazolam for general anesthesia induction in elderly patients. This study enrolled consecutive patients aged ≥ 65 with an American Society of Anesthesiologists (ASA) physical status I-III who underwent elective surgery. The 50% (50% effective dose [ED50]) and 90% (90% effective dose [ED90]) effective infusion rates of remimazolam for inducing general anesthesia were estimated using the k-in-a-row method. Successful anesthesia induction was defined as achieving a Modified Observer's Assessment of Alertness/Sedation (MOAA/S) score of ≤ 1 within 2 min of initiating remimazolam infusion. The initial infusion rate was set at 0.1 mg/kg/min, with subsequent adjustments made in increments/decrements of 0.02 mg/kg/min. According to the k-in-a-row method, the infusion rate increased after failure, but decreased only after k = 6 consecutive successes. A total of 50 patients were enrolled in this study. The estimated ED50 and ED90 for achieving an MOAA/S score ≤ 1 within 2 min from the start of remimazolam infusion were 0.10 mg/kg/min (90% CI [0.08-0.11]) and 0.13 mg/kg/min (0.12-0.19), respectively. Hemodynamic stability was maintained across all tested doses during the induction period, and none of the patients required vasopressors or inotropes. An infusion rate of 0.13 mg/kg/min of remimazolam effectively induces general anesthesia in elderly patients, while preserving hemodynamic stability.