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

Effects of Analgesia Nociception Index (ANI)-Guided Analgesia on Postoperative Bowel Function Recovery in Laparoscopic Colorectal Surgery: A Prospective Randomized-controlled Study

Investigators will examaine the effects of Analgesia Nociception Index (ANI)-guided analgesia on postoperative bowel function recovery in laparoscopic colorectal surgery. This is a prospective randomized-controlled study.

Investigators will randomly divide the patients into two groups. In ANI group, remifentanil infusion rate during anesthesia will be adjusted according to ANI monitoring. In Control group, remifentanil infusion rate during anesthesia will be adjusted according to the conventional method of blood pressure and heart rate monitroing. And Investigators will evalualte the bowel function recovery in both groups after surgery, and compare between the two groups.

Inclusion Criteria:

• Patients over 19 years who undergo laparoscopic colorectal surgery for colorectal cancer at Gangnam Severance Hospital, Seoul, South Korea.

Exclusion Criteria:

• Emergency surgery
• Patients with history of open abdominal surgery
• Patients with arrhythmia
• Patients with pacemaker insertion
• Patients with history of heart transplantation
• Patients taking medications that may affect ANI (antimuscarinics, alpha-agonists, beta blockers)
• Patients with chronic opioid medication.
• Cognitive impairment
• Unable to read consent form (eg illiterate, foreigner, etc.)