Inclusion Criteria:  Patients undergoing selective brain tumor resection surgery. Age ≥65 years. Obtain written informed consent.  Exclusion Criteria:  Preoperative severe cognitive impairment (mini-mental state examination, MMSE ≤ 20). Allergic to the study drug. body mass index ≤18 or ≥ 30 History of psychotropic 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 hepatic or renal dysfunction.