Effective bolus dose of remimazolam for i-gel^® insertion in nonparalyzed patients: a dose-finding study

Purpose: Remimazolam is a recently developed ultra-short-acting benzodiazepine used for anesthesia induction and maintenance. Nevertheless, the effective bolus dose of remimazolam for i-gel^® (Intersurgical Ltd., Wokingham, Berkshire, UK) insertion without the use of neuromuscular blocking agents (NMBAs) has not been well established. Methods: This study included 25 adult patients scheduled for surgery under general anesthesia who were eligible for i-gel use. Anesthesia was induced with predetermined bolus doses of remimazolam, starting at 0.3 mg·kg⁻¹ for the first patient, without the use of NMBAs. All patients concurrently received remifentanil using target-controlled infusion (TCI) at a fixed effect-site concentration (Ce) of 3.0 ng·mL⁻¹. Insertion of the i-gel was attempted 90 sec after remimazolam administration, and insertion conditions were assessed. Subsequent doses of remimazolam were decreased or increased by 0.05 mg·kg⁻¹, depending on the success or failure of i-gel insertion. Results: The mean (standard deviation) 50% effective dose (ED₅₀) of a remimazolam bolus for successful i-gel insertion as determined by the modified Dixon’s up-and-down method was 0.100 (0.027) mg·kg⁻¹. The ED₅₀ and ED₉₅ estimated by isotonic regression were 0.111 (83% confidence interval [CI], 0.096 to 0.131) mg·kg⁻¹ and 0.182 (95% CI, 0.144 to 0.195) mg·kg⁻¹, respectively. None of the patients required treatment for hypotension or bradycardia during anesthesia induction. Conclusion: Based on the ED₉₅ of remimazolam bolus dose determined in our study, we recommend using 0.182 mg·kg⁻¹ of remimazolam in combination with remifentanil TCI at a Ce of 3.0 ng·mL⁻¹ for successful i-gel insertion without NMBAs in adult patients. This regimen seems effective with a low risk of hemodynamic instability during anesthesia induction. Study registration: ClinicalTrials.gov (NCT05298228); first submitted 6 March 2022.