Step 2 of A Two-step Trial to Evaluate the Effectiveness and Safety of Remimazolam Besylate for Sedation in ICU Patients

Inclusion Criteria: * Age ≥ 18 and ≤ 80 years * Body mass index (BMI) ≥18 and ≤ 30 kg/m2 * Being Intubated and mechanically ventilated ≤48 hours before enrollment and expected to be on ventilator for at least 6 hours * Requirement for light to moderate sedation (a Richmond agitation-sedation scale score of -2 to 1) Exclusion Criteria: * Refusal to be included * Allergy or unsuitability to any composition of study drugs or remifentanil * Living expectancy less than 48 hours * Myasthenia gravis * Status asthmaticus * Abdominal compartment syndrome * Serious hepatic dysfunction (CTP 10-15); * Chronic kidney disease with glomerular filtration rate (GFR) \< 29 ml/min/1.73m2 * Mean blood pressure less than 65 mm Hg or the need of a continuous infusion of norepinephrine at ≥0.5 ug/kg/min to maintain Mean blood pressure ≥ 65 mm Hg * Possible requirement for surgery or bedside tracheostomy in 24 hours * Possible requirement for renal replacement therapy in 24 hours * Acute severe neurological disorder and any other condition interfering with sedation assessment * Abuse of controlled substances or alcohol * Pregnancy or lactation * Inclusion in another interventional trial in the past 30 days * Other conditions deemed unsuitable to be included