To explore the effect of daytime variation on postoperative hyperalgesia induced by opioids. Patients receiving endoscopy surgery under general anesthesia during 08:00-12:00(morning group, n=30) and 14:00-18:00(afternoon group, n=30) using remifentanil for anesthesia maintenance were respectively included. Postoperative hyperalgesia at PACU and 24 hours after surgery were assessed through mechanical pain measurement. Comparative analysis of postoperative hyperalgesia levels, pain and analgesic requirements between morning group and afternoon group were performed.

Inclusion Criteria:

• American Society of Anesthesiologists classification I-II
• Abdominal endoscopy surgery
• Estimated surgery duration 1-2h
• Right handedness
• Voluntarily receive postoperative intravenous controlled analgesia

Exclusion Criteria:

• Heavy smoking or alcohol dependence
• Puerpera or lactation women
• History of chronic pain
• Analgesic use within one month before surgery
• Allergy to opioids
• Can not follow with the study procedure

Patients receiving endoscopy surgery under general anesthesia during 08:00-12:00(morning group, n=30) and 14:00-18:00(afternoon group, n=30) using remifentanil for anesthesia maintenance were included.

The individual participant data for this study is available from the sponsor on reasonable request through email.