Optimizing the Subanesthetic Dose of Esketamine Combined with Propofol for Painless Gastroscopy in Adults: A Prospective Observational Study

Background: Propofol sedation is widely used for endoscopic procedures, but its administration alone poses risks of hemodynamic and respiratory depression. Esketamine, as an adjuvant, could reduce propofol requirements and associated adverse events. The median effective dose (ED ₅₀ ) of esketamine combined with propofol in adults undergoing painless gastroscopy remains undetermined. Therefore, we designed a study to determine the ED ₅₀ of esketamine combined with propofol using Dixon and Massey’s up-and-down sequential method to prevent somatic responses to endoscope insertion. Methods: Adult patients scheduled for elective painless gastroscopy who met the inclusion and exclusion criteria were enrolled. Following intravenous administration of esketamine, each participant received an initial propofol dose of 1.5 mg/kg. Esketamine dosing commenced at 0.2 mg/kg and was adjusted using a modified Dixon’s up-and-down method with a dose ratio of 1:1.2 (i.e., 20% increments/decrements) based on the preceding patient’s response to gastroscope insertion. Patient responses were categorized as: Failure: MOAA/S score > 1, swallowing, coughing, or purposeful movement. Success: Absence of the above reactions. If anesthesia induction failed, the esketamine dose was increased for the subsequent patient; if successful, the dose was decreased. The study continued until eight crossover points (failure-to-success transitions) were observed. The ED ₅₀ of esketamine was calculated as the mean of the crossover point doses. And in all patients, blood pressure, pulse oxygen saturation, heart rate, recovery time, and side effects were recorded. Results: A total of 29 adults undergoing elective painless gastroscopy were included. The ED ₅₀ of esketamine co-administered with 1.5 mg/kg propofol, determined via Dixon’s up-and-down method, was 0.172 mg/kg. Probit analysis estimated an ED ₅₀ of 0.159 mg/kg (95% CI: 0.144–0.176) and ED ₉₅ of 0.195 mg/kg (95% CI: 0.178–0.273). Time from induction to scope insertion was 31.6 ± 15.1 s, and total propofol dose was 114.01 ± 22.14 mg. Gastroscopy duration averaged 6.8 ± 2.1 min, with PACU stay time of 16.1 ± 3.7 min. Adverse events included transient sinus tachycardia (n = 1) and mild hypoxemia (SpO2% <90%; n = 1), with no serious adverse events. Conclusion: The ED ₅₀ of esketamine combined with 1.5 mg/kg propofol for painless gastroscopy was 0.172 mg/kg, as determined by Dixon's up-and-down sequential method. Trial registration This study was registered on 19 April 2023 at Chinese Clinical Trial Registry (http//www.chictr.org.cn registration NO. ChiCTR2300070635).