Remimazolam dose for successful insertion of a supraglottic airway device with opioids: a dose-determination study using Dixon’s up-and-down method

Purpose: Remimazolam, an ultra-short-acting benzodiazepine, was recently approved in numerous jurisdictions as an induction drug for general anesthesia. We aimed to determine the doses of remimazolam that would allow placement of a supraglottic airway device (SGD) in 50% and 95% of nonparalyzed patients (ED₅₀ and ED₉₅). Methods: In this prospective study, 30 American Society of Anesthesiology Physical Status I–II grade female patients scheduled for hysteroscopic surgery were enrolled. Anesthesia was induced with 1 μg·kg⁻¹ of fentanyl and continuous infusion of remimazolam without neuromuscular blockade. An i-gel® SGD was inserted 2.5 min after the start of remimazolam infusion. We used Dixon’s up-and-down method and isotonic regression to determine the ED₅₀ and ED₉₅ of remimazolam for insertion of an SGD. Results: Twenty-eight patients were included in the final analysis. The ED₅₀ and ED₉₅ of remimazolam required for successful i-gel insertion were 8.8 mg·kg⁻¹·hr⁻¹ (95% confidence interval [CI], 6.3 to 10.6) and 10.7 mg·kg⁻¹·hr⁻¹ (95% CI, 10.6 to 11.7), respectively. A nonfully relaxed jaw was found in 7/13 patients (54%) in the success group and 14/15 patients (93%) in the failure group (difference in proportions, 40%; 95% CI, 7 to 65; P = 0.02). Bucking or other movements during SGD insertion only occurred in the failure group (11/15, 73%). Conclusion: In 95% of nonparalyzed female patients undergoing hysteroscopy, 10.7 mg·kg⁻¹·hr⁻¹ of remimazolam with 1 μg·kg⁻¹ of fentanyl facilitates i-gel insertion. Remimazolam showed a high incidence of poor jaw relaxation and bucking or other movements during SGD insertion. Study registration: Clinical Trial Registry of the Republic of Korea (KCT0006527, https://cris.nih.go.kr; registered 1 September 2021; principal investigator: Ji Seon Jeong).