Inclusion Criteria:  Aged 18 years or older; Admitted to the ICU; With expected mechanical ventilation duration ≥12 hours; Meet the diagnostic criteria of sepsis (sepsis 3.0; patient with infection and a sequential organ failure assessment score ≥2).  Exclusion Criteria:  Refuse to participate in; Pregnancy; History of schizophrenia, epilepsy, parkinsonism, or myasthenia gravis; Inability to communicate (coma, profound dementia, or language barrier); Brain injury or neurosurgery; Left ventricular ejection fraction (LVEF) less than 30%, sick sinus syndrome, severe sinus bradycardia (<50 beats per min [bpm]), or second degree or greater atrioventricular block without pacemaker; Serious hepatic dysfunction (Child-Pugh class C); Serious renal dysfunction (undergoing dialysis); With expected survival for no more than 24 hours; Allergic to dexmedetomidine; Other conditions that were considered unsuitable for study participation.