Etomidate to Improve Outcome in Elderly Patients

Inclusion Criteria: * Aged between 65 and 80 years old. * Patients scheduled for elective gastrointestinal surgery under general anesthesia. Exclusion Criteria: * Expected duration of surgery \< 1 or \>4 hours * American Society of Anesthesiologists status \>III * Body Mass Index \< 18 kg/m2 or\> 25 kg/m2 * Cerebrovascular accident occurred within the previous 3 months,such as stroke or transient ischemic attack * Unstable angina and myocardial infarction occurred within the previous 3 months * Patients with serious hepatic dysfunction ( the serum level of alanine transaminase, conjugated bilirubin, aspartate transaminase, alkaline phosphatase or total bilirubin is 2 folds more than upper normal limit) or renal dysfunction(creatinine clearance rate less than 30 milliliter per minute). * Diabetic patients with complication (diabetic ketoacidosis, hyperosmotic coma,all kinds of infection, macroangiopathy, diabetic nephropathy, retinopathy, diabetic cardiomyopathy, diabetic neuropathy, diabetic foot). * Preoperative blood pressure more than or equal to 180/110 mmHg * Confirmed or suspected of narcotic analgesics abusing or long term using * Taking corticosteroids or immunosuppressive agents for more than 10 days with the previous 6 months or had history of adrenal suppression or immune system disease. * Patients with thyroid hypofunction. * Patients with history of asthma. * Patients with history of surgery within previous 3 months. * Patients allergic or contraindicated to propofol or etomidate * Patients participated in other study within the last 30 days