Objective:To evaluate the accuracy of surgical pleth index (SPI) in monitoring the depth of anesthesia in elderly patients undergoing general anesthesia.Methods:Thirty-five patients, of American Society of Anesthesiologists physical status Ⅰ or Ⅱ, aged 65-80 yr, with body mass index of 18-30 kg/m 2, scheduled for elective gynecological laparoscopic surgery, were studied.Combined intravenous-inhalational anesthesia was used to maintain bispectral index value at 45-60.SPI was recorded within 2 min before and after skin incision, before and after pneumoperitoneum, and before and after the most intense stimulation of skin incision.The maximum value (SPI max) within 2 min after noxious stimulation was recorded, and the difference between SPI max and baseline value (ΔSPI) was calculated.The receiver operating characteristic curve (ROC) was used to evaluate the accuracy of the above indicators in monitoring the depth of anesthesia. Results:Thirty patients were finally included in this study.The area under the curve of SPI max was 0.887, the diagnostic threshold was 57, the sensitivity was 68.9%, and the specificity was 92.9%.The area under the curve of ΔSPI was 0.988, diagnostic threshold was 12, the sensitivity was 88.0%, and the specificity was 98.7%. Conclusion:SPI can accurately determine the depth of anesthesia in elderly patients with general anesthesia, and using ΔSPI has more clinical significance.