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

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.

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.

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.

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.

ClinicalTrials.gov (NCT05298228); first submitted 6 March 2022.