Predisposing and precipitating factors for perioperative delirium for the elderly remain elusive. This research will be conducted to determine risk factors of postoperative delirium.
65 to 90 years old to receive elective major abdominal surgery (expected operation time over 2 hours); ,
American society of Aneshesiologists（ASA）physical status I-III;
Mini-Mental State Examination (MMES) score < 15;
Renal failure (requiring dialysis) or liver failure (Child-Pugh score > 5);
Severe impairment due to structural or hypoxic brain injury, more than 2 days in ICU one month before surgery;
Underwent major heart, lung or abdominal surgery within 1 year;