Background:
Currently, there is no gold standard for monitoring noxious stimulation during surgery, and the surgical pleth index (SPI) is only one of many monitoring methods. It is commonly used in the monitoring of conventional opiate anesthesia, but its effectiveness in opioid-free anesthesia (OFA) has not been evaluated. Therefore, the aim of this study was to observe the guidance value of the surgical pleth index in opioid-free anesthesia for patients undergoing lower abdominal or pelvic surgery.