The objective of this clinical trial is to investigate the efficacy and safety of oliceridine fumarate for analgesic treatment in mechanically ventilated subjects in the ICU. This study was conducted to answer the following questions (1) the efficacy of oliceridine fumarate for analgesic treatment in subjects with ICU mechanical ventilation (2) the safety of oliceridine fumarate for analgesic treatment in subjects with ICU mechanical ventilation. This study proposes to conduct a randomized controlled clinical trial in mechanically ventilated patients in the intensive care unit to compare the analgesic efficacy and incidence of adverse effects of two drugs, oliceridine fumarate injection and remifentanil. Subjects had an analgesic goal of CPOT <3 points and a sedation goal of RASS -2 to 0 points. Infusion syringes of remifentanil or oliceridine fumarate were prepared by a nurse according to the weight of the subjects. Subjects were enrolled in the group and were scored for analgesia and sedation related scores. Both groups received routine ICU monitoring and appropriate treatment, which was determined by the clinician.

Inclusion Criteria:

1. Patients aged ≥18 years and ≤80 years;
2. Admitted to the ICU and undergoing invasive mechanical ventilation with an expected duration of mechanical ventilation of more than 24 hours;
3. Subjects requiring sedation and analgesia;
4. Subjects or their guardians voluntarily participate in the study and sign an informed consent form;

Exclusion Criteria:

1. Pregnant or breastfeeding women;
2. Hypersensitivity to opioids (fentanyl, remifentanil, sufentanil, morphine, etc.);
3. Subjects with bronchial asthma attacks;
4. Subjects with acute intestinal obstruction;
5. Subjects who are unable to undergo RASS and CPOT assessments for various reasons, such as those with a history of psychiatric systemic disorders (schizophrenia, mania, psychosis, history of cognitive dysfunction), grand mal status epilepticus, and craniocerebral injury;
6. Severe hemodynamic instability (subjects who require administration of more than an equivalent dose of 0.5 μg/kg/min norepinephrine to maintain a MAP ≥ 65 mmHg and who, in the opinion of the investigator, are not suitable for enrollment);
7. Use of monooxygenase inhibitors (MAOIs) (see protocol appendix);
8. Chronic pain requiring long-term analgesic medication (duration of illness greater than 3 months);
9. Severe hepatic insufficiency (liver function in Child classification C);
10. Severe renal dysfunction (definition of renal dysfunction: chronic renal insufficiency [glomerular filtration rate (GFR) ≦29ml/(min1.73m3]; or long-term maintenance hemodialysis or peritoneal dialysis subjects);
11. Undergoing any clinical trial within 1 month prior to enrollment and receiving the test product;
12. ECG QT interval at screening: >450 ms for men and >470 ms for women;
13. Subjects with a desired sedation target RASS score within the range of -5 to -3 (including threshold) points;
14. Other conditions deemed unsuitable for enrollment by the investigator.