Effective doses of alfentanil combined with propofol for gastroscopy in patients of different ages under Narcotrend monitoring: a prospective dose-finding study utilizing the up-and-down sequential allocation method.

Background: Painless gastroscopy is preferred by both patients and physicians, as it minimizes discomfort during the procedure. Alfentanil, a short-acting opioid analgesic, possesses pharmacological properties that make it suitable for inducing analgesia during gastroscopy. However, research on the optimal dosage of alfentanil when used in combination with propofol for gastroscopy is limited. Therefore, this study aimed to investigate the 50% and 95% effective doses (ED50 and ED95, respectively) of alfentanil in combination with propofol for gastroscopy, using Narcotrend monitoring.

Methods: Elective gastroscopy was performed in 51 patients aged 18-80 years, with a body mass index of 18-28 kg/m², and American Society of Anesthesiologists Class I or II. Based on their age, they were categorized into the youth group (18-60 years) and the elderly group (61-80 years). The patients were connected to the vital signs monitor and Narcotrend, and propofol was administered intravenously until the Narcotrend index was at Stage C1-C2 (65-74) and had stabilized for 1 min. Following this, alfentanil was administrated (initial dose, 5 µg/kg); if a positive reaction to the gastroscope placement was elicited, the dose was increased to a higher level in the next patient; otherwise, the dose was decreased to a lower level, with a dose gradient of 0.5 µg/kg. Gastroscope insertion was started 90 s later, and the criteria for a positive reaction to gastroscope insertion included coughing, nausea, and/or motor reaction during or within 1 min of gastroscope insertion. The test was stopped if seven folds occurred during the study. The ED50 values with their 95% confidence intervals (CIs) of alfentanil in combination with propofol for the inhibition of gastroscopic placement were calculated.

Results: Under the sedation conditions induced using alfentanil and propofol and detected using Narcotrend, the ED50 (95% CI) were 5.39 µg/kg (4.76-6.47) in the youth group and 5.69 µg/kg (4.67-6.31) in the elderly group, respectively.

Conclusions: The ED50 of alfentanil combined with propofol for gastroscopy under Narcotrend monitoring were 5.39 µg/kg in the youth group and 5.69 µg/kg in the elderly group, respectively.