Inclusion Criteria:  patient's age was 65 yr or older patient was scheduled to undergo elective major laparoscopic abdominal surgery (e.g., gastrointestinal and gynecologic surgery). the surgery was expected to last 2h or longer.  Exclusion Criteria:  severe diseases in cardiovascular, respiratory, liver, kidney, or central nervous systems and having a life span of less than 3 months; a mini-mental status examination score (MMSE) of less than 23; a history of dementia or psychiatric illness; current use of sedatives, antidepressants or corticosteroids; alcoholism and drug dependence; difficulty with follow-up or poor compliance; patients with preoperative sleep disturbances; patients with sleep apnea or moderate and severe obstructive sleep apnea-hypopnea syndrome (OSAHS); patients with severe visual or hearing impairment or who were unable to communicate.