Effective remimazolam loading dose for adequate sedation in regional anesthesia

Purpose Remimazolam is a novel ultrashort-acting sedative considered appropriate for continuous infusion during surgical procedures. Nevertheless, information regarding its loading dose for sedation during surgery is limited. We aimed to determine the 90% effective dose (ED 90 ) of the remimazolam loading dose for sedation in patients undergoing limb surgery under regional anesthesia. Methods We included 50 patients aged 19–80 yr undergoing limb surgery under regional anesthesia. After regional anesthesia, remimazolam besylate was administered at the assigned dose. For ten minutes after the initiation of loading, the level of sedation was evaluated using the Modified Observer’s Assessment of Alertness/Sedation (MOAA/S) scale. The primary outcome was the ED 90 based on whether patients reached a MOAA/S score of ≤ 3 points (loss of response to verbal command) within ten minutes. The secondary outcomes were the ED 50 and the estimated effect site and plasma concentration at the time of achieving successful sedation. Results In total, 49 patients were included in the final analysis, and adequate sedation with the assigned loading dose was successful in 42 patients. The log-logistic function showed that the ED 90 and ED 50 were 0.617 mg·kg −1 ·hr −1 (95% confidence interval [CI], 0.511 to 0.722; 98% CI, 0.492 to 0.741) and 0.438 mg·kg −1 ·hr −1 (95% CI, 0.335 to 0.541; 98% CI, 0.315 to 0.560), respectively. Conclusion The ED 90 of the remimazolam loading dose to achieve adequate sedation in patients undergoing limb surgery under regional anesthesia was 0.617 mg·kg −1 ·hr −1 (95% CI, 0.511 to 0.722; 98% CI, 0.492 to 0.741). Study registration ClinicalTrials.gov (NCT05340335); first posted 22 April 2022.