Clinical Research Directory

Inclusion Criteria: * Age ≥65 years old; * Admitted to intensive care unit (ICU) after noncardiac surgery; * Expected to stay in ICU until the next morning. For those with endotracheal intubation, the expected duration of mechanical ventilation is \<24 hours; * Provide written informed consents. Exclusion Criteria: * Preoperative history of schizophrenia, epilepsy, Parkinsonism, or myasthenia gravis; * Inability to communicate in the preoperative period (coma, profound dementia, or language barrier); * Preoperative history of sleep apnea (previous diagnosis; or STOP-Bang score ≥3 with serum bicarbonate ≥ 28 mmol/L); * Known sick sinus syndrome, severe sinus bradycardia (\<50 beats per min \[bpm\]), or second degree or higher atrioventricular block without pacemaker; * Hypotension (systolic blood pressure \[SBP\] \<90 mmHg, mean arterial pressure \[MAP\] \<70 mmHg, or a decrease of SBP \>30% of baseline) or in a state of shock (vasopressors are required to maintain MAP ≥65 mmHg and serum lactate \>2 mmol/L); * Severe hepatic dysfunction (Child-Pugh class C), renal failure (requirement of renal replacement therapy), or expected survival \<24 hours; * Traumatic brain injury or neurosurgery; * Presence of delirium before surgery (assessed with Confusion Assessment Method \[CAM\]/CAM-ICU); * Undergoing treatment of dexmedetomidine or clonidine; * Other conditions that are considered unsuitable for study participation.