Comparison of the ED<sub>90</sub> of Esketamine for Suppressing Laryngeal Mask Airway Insertion Responses During Propofol Induction with or without Intravenous Lidocaine Pretreatment: A Randomized Double-Blind Dose-Finding Trial.

Abstract

<h4>Background</h4>Esketamine has been increasingly used as an adjunct to propofol induction because of its analgesic and sympathomimetic properties. However, the ED₉₀ of esketamine for suppressing laryngeal mask airway (LMA) insertion responses under a fixed propofol background, with or without intravenous lidocaine pretreatment, remains unclear. This study aimed to determine and compare this ED₉₀ in patients receiving intravenous lidocaine or normal saline.<h4>Methods</h4>In this randomized, double-blind, dose-finding trial, adult patients undergoing elective arthroscopic shoulder surgery received intravenous lidocaine 1 mg·kg^-1 (Group L) or an equal volume of normal saline (Group N) before anesthesia induction. Thirty seconds later, esketamine was administered according to a biased coin design, followed by propofol 2 mg·kg^-1. LMA insertion responses were assessed using a predefined four-item behavioral scoring system, and successful suppression was defined as a total score of 4. Enrollment continued until at least 45 effective responses were obtained in each group. The primary outcome was the ED₉₀ of esketamine, estimated by centered isotonic regression with bootstrap confidence intervals.<h4>Results</h4>Ninety-nine patients completed the study. The estimated ED₉₀ of esketamine was 0.173 mg·kg^-1 (95% CI, 0.138-0.209 mg·kg^-1) in Group L and 0.229 mg·kg^-1 (95% CI, 0.190-0.263 mg·kg^-1) in Group N, with an absolute between-group difference of -0.056 mg·kg^-1 (95% CI, -0.102 to -0.002 mg·kg^-1). Compared with Group N, Group L also showed lower heart rate immediately before and 3 min after LMA insertion, as well as a lower incidence of tachycardia. Other peri-induction adverse events were similar between groups.<h4>Conclusion</h4>Intravenous lidocaine pretreatment was associated with a lower ED₉₀ of esketamine for suppressing LMA insertion responses during propofol induction, suggesting an esketamine-sparing effect within this specific induction framework.

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