Inclusion Criteria:  Adults who are treated with sedation and analgesia for invasive mechanical ventilation  Exclusion Criteria:  they have baseline severe cognitive impairment; were pregnant or breast-feeding; were blind, deaf ; had second-degree or third-degree heart block or bradycardia requiring intervention; had an allergy to the experimental drugs; had an indication for benzodiazepines; were anticipated to have immediate discontinuation of mechanical ventilation; were expected to have neuromuscular blockade for more than 48 hours; were in a moribund state; or had received mechanical ventilation for more than 96 hours before meeting all inclusion criteria.