Intraoperative Infusion of Dexmedetomidine for Prevention of Postoperative Delirium in Elderly Patients

Inclusion Criteria: * Patients undergoing selective craniotomy. * Age ≥65 years. * Obtain written informed consent. Exclusion Criteria: * Operation time less than 2 hours. * Refusal to provide written informed consent. * Cognitive impairment before surgery(mini-mental state examination, MMSE ≤ 26 or Montreal Cognitive Assessment, MoCA≤22). * Allergic to the study drug. * Body mass index ≤18 or ≥ 30 kg/m2. * History of psychotropic drugs, anticholinergic drugs, antihistamine drug and dopaminergic drugs. * History of traumatic brain injury or neurosurgery. * Severe bradycardia (heart rate less than 40 beats per minute), sick sinus syndrome or second-to-third degree atrioventricular block. * Severe liver dysfunction (Child-Pugh grade C) or renal failure (requiring kidney replacement therapy). * The functional neurosurgery.