The purpose of this study is to evaluate the efficacy and safety of Tegileridine Fumarate lnjection for prolonged abirritation(48h to 72h) during mechanical ventilation in the ICU.

Inclusion Criteria:

1. Patients or their guardians are able to provide a written informed consent
2. Subjects have been treated with endotracheal intubation and mechanical ventilation ≤24h, and then prolonged mechanical ventilation ≥48h in the next
3. Age ≥ 18 and ≤ 85 years, Male or female
4. Body mass index (BMI) > 18 and < 30 kg/m2
5. Use of highly effective contraception for a specified period if applicable

Exclusion Criteria:

1. Those who are known or suspected to be allergic or contraindicated to various components of the experimental drugs involved in the research institute
2. With an expected survival time of less than 48 hours
3. unable to undergo CPOT and RASS assessments due to various reasons, such as a history of psychiatric disorders, neurological disorders, neurological dysfunction, and consciousness disorders, as well as blindness, deafness, or aphasia
4. Myasthenia gravis, bronchial asthma attack, acute intestinal obstruction, abdominal compartment syndrome
5. Multiple organ failure
6. Malignant tumor Subjects who received radiotherapy, chemotherapy, targeted therapy, and immunotherapy within the first month of randomization
7. Chronic pain requires long-term use of analgesics
8. Severe liver dysfunction
9. Severe renal dysfunction
10. Severe renal dysfunction
11. Need to receive deep sedation or use neuromuscular blocking drugs
12. Surgery or tracheotomy may be required during the study administration period
13. Used monoamine oxidase inhibitors within the two weeks randomization
14. History of drug abuse, drug use, alcohol abuse, and long-term use of psychotropic drugs within 2 years prior to the start of the screening period
15. QTc abnormality during screening period
16. Positive result for infectious disease
17. Positive screening for drug abuse
18. Pregnant or nursing women;
19. Subjects who has Participated in any other clinical trials within the first 3 months of randomization
20. Other conditions deemed unsuitable to be included.