Post-operative cognitive dysfunction (POCD) is a fairly well-documented clinical phenomenon. Most patients will receive general anesthesia during surgery. Two groups of general anesthetics are used for this purpose. We hypothesize that the incidence of POCD is not different in patients received intravenous anesthetics only or sevoflurane (a volatile anesthetic-based general anesthesia) for their major intra-abdominal surgery.

Patients who are 60 years old or older for laparoscopic abdominal surgery will be randomly assigned into two groups: 1) sevoflurane-based general anesthesia group, and 2) propofol-based general anesthesia group. Each group will need 221 patients to detect 1/3 of decrease or increase in the rate of POCD of one group compared with another group at about one week after surgery, assuming the overall rate of POCD at this time is about 40% at this time. Considering about 10% loss to follow-up, we will have 250 patients in each group. In addition, investigators will need 184 subjects in the control group. The data of these control subjects will be used to normalize the data of the two studied groups to diagnose POCD. The subjects in control groups will also be elderly but without the exposure to anesthesia and surgery.

Inclusion Criteria:

1. major elective gastrointestinal, gynecological, prostate or bladder surgery patients who are ≥ 60 years old.
2. the surgery is laparoscopic surgery and is expected to last for ≥ 2 hours under general anesthesia and the patient will stay in hospital for at least 7 days after surgery.
3. lack of serious hearing and vision impairment and be able to read so that neurobehavioral tests can be performed.

Exclusion Criteria:

1. Patients are not expected to be alive for longer than 3 months.
2. Mini-mental State Examination (MMSE) [18] score ≤ 23.
3. history of dementia, psychiatric illness or any diseases of central nervous system.
4. current use of sedatives or antidepressant.
5. alcoholism and drug dependence.
6. patients previously included in this study (for patients who have second intra-abdominal surgery during the study period).
7. difficult to follow up or patients with poor compliance.
8. uncontrolled hypertension (> 180/100 mmHg)