Tegileridine
DrugParticipants in this arm will receive postoperative analgesia via a Patient-Controlled Intravenous Analgesia (PCIA) pump containing a sterile solution. The pump is filled with a 100 mL mixture of the investigational drug, Tegileridine Fumarate Injection, at a concentration of 0.05 mg/mL, and the adjuvant drug, Dexmedetomidine Hydrochloride Injection, at 2 μg/mL. The PCA pump is programmed with no continuous background infusion (0 mL/h). A loading dose of 20 mL is administered at the start. Thereafter, participants can self-administer a 4 mL bolus on-demand for pain relief, with a maximum allowable dose of 12 mL per hour and a lockout interval of 10 minutes between boluses. This intervention is planned for a duration of 72 hours following abdominal surgery.