Inclusion Criteria:  Intubated in the past 24 hours with invasive mechanical ventilation Expected to continue mechanical ventilation for more than 48 hours Informed consent/assent was obtained from all patients or their representatives  Exclusion Criteria:  Patients with a history of allergy to opioids, benzodiazepines, propofol, or alcohol/drug abuse were excluded from the study Patients who are known or suspected to be allergic to the study drug Patients whose expected survival time is less than 48h Patients receiving deep sedation (RASS≥-4) Patients using neuromuscular blocking agent Patients who cannot be assessed by RASS Patients with myasthenia gravis patients with bronchial asthma patients with abdominal compartment syndrome Patients who need surgery or tracheotomy during the study drug treatment period Women during pregnancy and lactation Patients who have used short-acting non-steroidal anti-inflammatory drugs within 6 hours Patients who have used long-acting non-steroidal anti-inflammatory drugs within 12 hours Patients with a history of chronic pain for more than 3 months or who are receiving regular analgesia for more than 3 months Patients who have used monoamine oxidase inhibitors within two weeks Patients who participate in any clinical trials as subjects within 1 month Patients with a history of drug abuse, drug abuse, alcohol abuse* and long-term use of psychotropic drugs within 2 years Alcoholism: Drinking more than 14 times/week (1 time=150ml wine or 360ml beer or 45ml spirits)