Postoperative agitation (hyperactive delirium) is common following major surgery(incidence was about 20% in our pilot study). Dexmedetomidine was related to a reduced delirium rate when comparing with midazolam in many clinical settings. It is not clear if dexmedetomidine is useful on reducing postoperative delirium. The hypothesis of present study: intraoperative application of dexmedetomidine (0.2ug/kg/h) is is effective (50% reduce) than placebo for reducing of early postoperative delirium and increase postoperative quality of recovery within 24 postoperative hours.

After approval from the Institute's Ethics Committee, this study was conducted at Tongji Hospital, a general university teaching hospital with 2500 beds in Wuhan, China.The study consisted of adult patients, American Society of Anaesthesiologists Physical Status (ASA-PS) I-III, undergoing selective major surgery under general anesthesia. All the patients were randomly assigned to receive dexmedetomidine or placebo during the operation. The primary outcome measure was postoperative delirium assessed by Nursing Delirium Screening Scale (Nu-DESC) every 8 hours within 24 postoperative hours. The secondary outcome was length of postanesthesia care unit (PACU) stay,postoperative hospital length of stay, hemodynamic parameters, the incidence of postoperative nausea and vomiting, and quality of recovery determined by quality of recovery (QOR40; maximum score 200)and Post-operative Quality Recovery Scale (PQRS) in the first 24 h after surgery.

Inclusion Criteria:

• ASA physical status class I-III
• Aged 60 years or above
• Elective major surgery under general anesthesia

Exclusion Criteria:

• ASA-PS>=IV
• Aged under 60 yr old
• Body mass index (BMI) >30
• Neurologic disease
• Cardiac surgery and neurologic surgery
• Anticonvulsant drugs
• Chronic analgesics intake
• Participating in the investigation of another study