This study evaluates the effects of Analgesia Nociception Index (ANI)-guided intraoperative analgesia on postoperative pain in patients undergoing open gynecologic surgery.

Postoperative pain is one of the most common postoperative complications and is significantly associated with patient's quality of recovery. Analgesia Nociception Index (ANI) is known to analyze the high frequency component of heart rate variability in relation to respiratory frequency, providing the objective information on the degree of pain. However, most previous studies conducted by using ANI were observational studies or small-sized randomized controlled studies. In the present study, the investigators aimed to evaluate the effects of ANI-guided intraoperative analgesia on moderate-to-severe postoperative pain by performing randomized controlled study.

Inclusion Criteria:

• Age ≥ 18
• Elective open gynecological surgery
• American Society of Anaesthesiologists physical status classification 1-3

Exclusion Criteria:

• Laparoscopic surgery or robot-assisted surgery
• Patients who had analgesic agents, anti-psychotic agents, anticonvulsants which were related to chronic pain
• Patients who had hypersensitivity to analgesic agents or medications related anesthesia.
• Patients who were required to have mechanical ventilation after surgery
• Patients who had arrhythmia
• Patients who transferred to the surgical intensive care unit immediately after surgery
• Pregnancy