Evaluation of Safety and Efficacy of Nalbuphine Versus Morphine for Postoperative Analgesia

Inclusion Criteria: 1. Age 18-65 years (inclusive), regardless of gender. 2. Weight 45-100 kg (inclusive) and BMI 18.0-30.0 kg/m² (inclusive). 3. Preoperative ASA Physical Status Class I-III. 4. Scheduled for elective general anesthesia in abdominal surgery (single incision ≥5 cm) or orthopedic surgery (limb/joint procedures); completed anesthesia recovery within 4 hours postoperatively, with NRS score ≥4, and willingness to accept protocol-defined analgesia. 5. Ability to comprehend study objectives, operate PCIA devices, and communicate effectively with investigators. 6. Female subjects must be non-pregnant, non-lactating, and agree to use contraception (including partners) for 3 months post-study. 7. Voluntary participation with signed informed consent. Exclusion Criteria: 1. Known or suspected allergy/hypersensitivity to any component of the investigational product, other opioids, or contraindicated drugs specified in the protocol . 2. Neurological/psychiatric disorders including: 1. Clinically significant neurological diseases (e.g., epilepsy, cognitive impairment) . 2. History of brain injury, increased intracranial pressure, or psychiatric disorders (e.g., schizophrenia, bipolar disorder, depression, anxiety) that may interfere with safety or study assessments as judged by the investigator . 3. Cardiovascular diseases/history: 1. Severe cardiovascular conditions (NYHA Class II or higher), myocardial infarction, angina, or severe arrhythmia within the past year . 2. Abnormal 12-lead ECG findings during screening (e.g., sinus bradycardia ≤55 bpm, ≥Grade II AV block) deemed unsuitable by the investigator . 3. Resting systolic blood pressure ≥160 mmHg or \<90 mmHg, diastolic ≥100 mmHg pre-surgery . 4. Intraoperative circulatory instability (e.g., hypotension, bradycardia) assessed as high-risk for trial continuation . 4. Respiratory disorders/history: 1. Bronchial asthma, high-risk respiratory depression conditions (e.g., severe COPD ≥GOLD 3, sleep apnea syndrome) . 2. Preoperative SpO2 \<93% (room air) or intraoperative respiratory depression/ventilatory dysfunction deemed unsafe . 5. Paralytic ileus, biliary/pancreatic diseases within 12 months before screening . 6. Major surgery within 3 months prior to screening. 7. Acute/chronic non-surgical pain interfering with postoperative pain assessment . 8. Preoperative anemia: Hemoglobin \<70 g/L or hematocrit \<25% . 9. High bleeding risk: 1. Congenital bleeding disorders (e.g., hemophilia) . 2. Platelet count \<0.75×LLN, PT \>ULN+3s, or APTT \>ULN+10s . 10. Organ dysfunction: 1. Albumin \<35 g/L (untreated) . 2. Liver/kidney function abnormalities: TBIL/ALT/AST/ALP ≥1.5×ULN ; Creatinine ≥1.5×ULN or clinically significant renal impairment; Recent dialysis (within 28 days) . 11. Random blood glucose ≥11.1 mmol/L during screening (preoperative) . 12. Participation in other clinical trials with active treatment within 3 months before surgery . 13. Other conditions deemed unsuitable by the investigator for safety or protocol compliance.