The primary objective is to evaluate the analgesic efficacy and safety of IV YZJ-4729 Tartrate Injection in patients with acute postoperative pain following Orthopedic surgery

Inclusion Criteria:

1. Be able to understand the study purpose and cooperate with the study procedures of this trial, voluntarily provide written informed consent
2. BMI≥18.0 kg/m2 and ≤28.0 kg/m2
3. ASA I to II
4. Experiences a pain intensity rating of moderate to severe acute pain following orthopedic surgery, with a pain intensity score of ≥4 on a Numeric Rating Scale (NRS) within 4 hours post-surgery

Exclusion Criteria:

1. Opioid allergy
2. Nervous system diseases (e.g. epilepsy)
3. Psychiatric disorders (e.g. depression)
4. History of difficult airways
5. Random blood glucose ≥11.1 mmol/L
6. Subjects with systolic blood pressure >160 mmHg and/or diastolic blood pressure >100 mmHg or systolic blood pressure < 90 mmHg
7. Abnormal pulse oxygen saturation (SpO2 <92 %)
8. Abnormal liver function or renal function
9. Used agents that could affect the analgesic response
10. Used agents that could affect drug metabolism
11. Has previously participated in another YZJ-4729 clinical study