Effects of Analgesia Nociception Index (ANI)-Guided Analgesia on Postoperative Bowel Function.

Investigators will attach the ANI monitor V2 (MDoloris Medical Systems, Lille, France) to the patient and monitor Analgesia Nociception Index (ANI) during anesthesia. Remifentanil infusion rate is adjusted according to ANI monitoring. The ANI is adjusted to be between 50 and 70.

Remifentanil infusion rate is adjusted according to the conventional method of blood pressure and heart rate monitroing. Blood pressure and heart rate are controlled to be within 20% of baseline. Investigators will not monitor ANI in this group.