Night-time Dexmedetomidine-esketamine Infusion and Sleep Quality in ICU Patients

Inclusion Criteria: * Aged 50 years or older; * Admitted to the intensive care unit (ICU) after surgery; * Receiving mechanical ventilation or high-flow nasal cannula oxygen therapy during night-time (after 6 pm), with an expected duration of ≥12 hours. Exclusion Criteria: * Duration of invasive/non-invasive ventilation ≥12 hours before enrollment; * Planning to receive muscle relaxant treatment; * History of schizophrenia, epilepsy, Parkinson's disease, or myasthenia gravis; * Unable to communicate due to coma, delirium, severe dementia, or language barrier before receiving mechanical ventilation or high-flow nasal cannula oxygen therapy; * Acute stroke or hypoxic encephalopathy, or after craniocerebral injury or neurosurgery; * Comorbid with hyperthyroidism or pheochromocytoma; * Taking sedative/hypnotic drugs or analgesics regularly (for more than 1 week) in the last month; * LVEF\<30%; sick sinus syndrome, severe sinus bradycardia (heart rate\<50 beats/min), atrioventricular block of more than II degree and without pacemaker; or systolic blood pressure \<90 mmHg despite vasopressor infusion; * Severe liver dysfunction (Child-Pugh C grade), severe renal dysfunction (dialysis), or estimated survival ≤24 hours; * Diagnosed obstructive sleep apnea, or body mass index \>30 kg/m2; * Allergies to dexmedetomidine and/or esketamine, or other conditions that are considered unsuitable for study participation; * Enrolled in other clinical studies.