Effect of es-ketamine for postoperative analgesia on postoperative gastrointestinal dysfunction in elderly colorectal cancer: a prospective, single-center, randomized, controlled study

Interventions: E-S group:1.5 mg/kg es-ketamine plus 3 µg/kg for postoperative venous self-controlled analgesia;S group:3 µg/kg for postoperative venous self-controlled analgesia Primary outcome(s): Duration of postoperative ileus: time from the end of surgery to the first postoperative bowel movement Study Design: Parallel