Safety Study of Dexmedetomidine in Elderly Under General Anesthesia

Inclusion Criteria: * age ≥65yr, American Society of Anesthesiologists (ASA) physical status scale grade I-III, ready for HP; body weight between 45 and 75kg, body mass index (BMI) between 18 and 24kg/m2; * the health conditions generally well according to medical history, physical examination, and laboratory tests; * no signs of difficult intubation; * no history of dementia and mental problems; * normal cognitive function, ability to understand and comply with study procedures. Exclusion Criteria: * Age \<65 yr or \>90 yr; BMI greater than 24 kg/m2; ASA grade higher than III; * Heart failure, severe arrhythmias, severe bradycardia (heart rate less than 40 beats/min), atrioventricular block of degree 2 or above, sick sinus syndrome, systolic blood pressure (SBP) ≥180 or \<90 mmHg, diastolic blood pressure (DBP) ≥110 or \<60 mmHg; * Severe liver or kidney dysfunction, severe infection, and other pathological conditions that interfere with study results. * Dementia, cerebrovascular accidents within 3 months, mental illness, epilepsy, and other adverse events that interfere with study results. * Patients with the conditions that block communication and preoperative assessment, such as serious hearing or visual impairment; * History of chronic analgesic use, long-term psychotropic medication use, alcohol or drug addiction.