The goal of this clinical trial is to compare the safety and efficacy of fospropofol and propofol during sedation in invasively mechanically ventilated patients in the Anesthesia Intensive Care Unit (AICU). Specific objectives include the following:

• Evaluate the sedative effects of fospropofol and propofol in invasively mechanically ventilated patients. Compare the sedative effects of the two medications using relevant clinical indicators and scoring tools, such as the Richmond Agitation-Sedation Scale (RASS).
• Compare the safety of fospropofol and propofol during sedation. Monitor medication-related adverse reactions, such as respiratory depression, hypotension, arrhythmias, headache, injection site pain, and assess the differences in adverse reaction incidence between the two medications.
• Compare the characteristics of recovery from sedation between PPD and propofol. Focus on the time from sedation to emergence from sedation and compare the differences in recovery time between the two medications.

Participants will be sedated with fospropofol or propofol during invasive mechanical ventilation.

Inclusion Criteria:

1. Aged 18-75 years old
2. Intubation and mechanical ventilation <12h before enrollment
3. Expected to require continuous invasive ventilation and sedation less than 6h after admission to anesthesia intensive care unit (AICU).
4. Signed informed consent

Exclusion Criteria:

1. parturient, childbirth or lactating mothers
2. acute severe neurological disease or coma
3. chronic renal failure
4. previous mechanical ventilation >12h
5. severe liver dysfunction (Child-Pugh score C)
6. BMI >30kg/m2 (>90kg)
7. dying