Objective:To evaluate the efficacy of adjusted Narcotrend Index (NI) value guidancecombined with small-dose esketamine for program-controlled closed-loop target-controlled infusion (TCI) system.Methods:Forty-eight American Society of Anesthesiologists Physical Status classificationⅠ or Ⅱpatients, regardless of gender, aged 18-55 yr, with body mass index of 18-25 kg/m 2, scheduled for elective laparoscopic surgery under general anesthesia, were assigned to control group (group C, NI baseline value median 36) and esketamine group(group E, NI baseline value median 46) using a random number table method, with 24 cases in each group. Anesthesia induction and maintenance were carried out using effect-site concentration TCI(Schnider model for propofol infusion and Minto model for remifentanil infusion). After the NI value was maintained at 26-46 during anesthesia maintenance, a small dose of esketamine was given (as an intravenous bolus 0.2 mg/kg, followed by an infusion of 5 μg·kg -1·min -1for 30 min) in group E, and the equal volume of normal saline was given instead in group C. Program-controlled closed-loop TCI was then started, and the target effect-site concentrations of propofol and remifentanil were adjusted every 5 min according to the corresponding preset NI baseline value. The main outcome measures were the percentage of time of NI value maintained in the target range within 1 h after administration of esketamine. Secondary outcome measures were the consumption of propofol and remifentanil, postoperative recovery time, incidence of nausea and vomiting, pain and shivering within 1 h after surgery. Patients were followed for intraoperative awareness on 2nd day after operation. Results:The performance of the program-controlled closed-loop TCI systems was within the safe clinical threshold, with no intraoperative awareness occurred in both groups. The consumption of propofol and remifentanil was significantly reduced in group E as compared to group C( P<0.05). There were no statistically significant differences in the percentage of time of NI value maintained in the target range, postoperative recovery time and incidence of adverse reactions between the two groups ( P>0.05). Conclusions:Adjusted NI value guidance combined with small-dose esketamine provides better efficacy when used for program-controlled closed-loop TCI system.