PostoperAtive Neurocognitive Dysfunction After Major AbdomiNal Surgery (PANDAMAN)

Inclusion Criteria: 1. 65 to 90 years old to receive elective major abdominal surgery (expected operation time over 2 hours); , 2. American society of Aneshesiologists（ASA）physical status I-III; Exclusion Criteria: 1. Mini-Mental State Examination (MMES) score \< 15; 2. Renal failure (requiring dialysis) or liver failure (Child-Pugh score \> 5); 3. Severe impairment due to structural or hypoxic brain injury, more than 2 days in ICU one month before surgery; 4. Underwent major heart, lung or abdominal surgery within 1 year; 5. Positive for Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or symptomatic (e.g. fever, cough, loss of taste/smell); 6. The cognitive assessment cannot be completed because the subject is blind, deaf, or unable to communicate in the local language; 7. Long-term follow-up unavailable (homelessness, active psychosis or substance abuse).