Inclusion Criteria:  Major abdominal surgery patient operated by laparotomy (predicted operative time ≥ 2 hours) epidural analgesia accepted  Exclusion Criteria:  Minor or protected patient Patients under guardianship, curatorship or safeguard of justice Pregnant or breastfeeding woman Contraindication or refusal of epidural analgesia Failure of the initial placement of the epidural catheter Major intraoperative complication requiring continued postoperative sedation