Title: Effect of Tegileridine on Postoperative Bowel Function Recovery in Abdominal Surgery: A Multicenter, Randomized, Controlled Trial

The goal of this clinical trial is to evaluate the effectiveness and safety of tegileridine, a biased μ-opioid receptor agonist, for patient-controlled intravenous analgesia (PCIA) after abdominal surgery.

The main question it aims to answer is:

Is tegileridine superior to morphine in promoting the recovery of gastrointestinal function within 72 hours after abdominal surgery?

Researchers will compare the experimental group (receiving Fumarate Tegileridine Injection) to the active control group (receiving Morphine Hydrochloride Injection). Both groups will also receive dexmedetomidine in their PCIA pumps. This comparison will determine if tegileridine is more effective for bowel recovery and has a better safety profile.

Participants who are scheduled for elective abdominal surgery under general anesthesia will:

1. Be randomly assigned to receive either a tegileridine-based or a morphine-based pain relief pump after surgery.
2. Use the patient-controlled analgesia (PCA) pump for up to 72 hours postoperatively to manage their pain.
3. Be assessed for the time it takes for their bowel function to return (tolerating food and having gas or bowel movement).
4. Have their pain levels, overall recovery quality, sleep quality, and any side effects monitored during hospitalization.
5. Be followed up 30 days after surgery.

Inclusion Criteria:

1. Scheduled to undergo elective abdominal surgery under general anesthesia.
2. Age ≥ 18 years.
3. Body Mass Index (BMI) between 18 and 30 kg/m².
4. American Society of Anesthesiologists (ASA) physical status classification of I to III.
5. Requires postoperative analgesia and is capable of correctly using a patient-controlled intravenous analgesia (PCIA) pump.
6. Understands the trial objectives and voluntarily participates, providing written informed consent.

Exclusion Criteria:

1. Undergoing gastrointestinal tract surgery.
2. Has advanced cancer with ascites or extensive metastasis, or is receiving systemic chemotherapy/radiotherapy, or requires postoperative hyperthermic intraperitoneal chemotherapy (HIPEC).
3. Diagnosed or suspected gastrointestinal obstruction or emptying disorder.
4. History of severe cardiovascular or cerebrovascular disease (e.g., severe sinus bradycardia, myocardial infarction, unstable angina, grade II or higher atrioventricular block, history of arrhythmia, NYHA class II or higher heart failure, ischemic stroke) or abnormal QTcF interval at screening ( >450 ms for males, >470 ms for females).
5. Comorbid psychiatric or neurological disorders (e.g., schizophrenia, depression, epilepsy) or cognitive dysfunction.
6. Known allergy to opioid drugs or any component of the trial medications.
7. Current acute or chronic pain conditions, or presence of hyperalgesia or other sensory disorders.
8. Long-term opioid therapy (defined as receiving >15 mg morphine milligram equivalents per day for more than 3 days per week, over a period exceeding 1 month within the 12 months prior to surgery).
9. Pregnant or breastfeeding women, or those with a positive pregnancy test at screening or on the day of surgery; or participants (including males) planning for pregnancy.
10. Significant hepatic or renal dysfunction (e.g., ALT/AST > 3 times the upper limit of normal, or requiring renal replacement therapy).
11. Planned admission to the Intensive Care Unit (ICU) for postoperative management.
12. Participation in another interventional clinical trial within the 3 months prior to randomization.
13. Any other condition deemed by the investigator as unsuitable for participation in this trial.