Postoperative delirium has been found to be associated with increased risk of future neurocognitive decline and mortality especially in elderly patients. Similarly, Frailty has been found to be associated with an increased risk of postoperative complication including delirium in the elderly.The purpose of this study is determine the factors affecting the incidence of postoperative delirium in frail elderly undergoing non-cardiac surgery in the Singapore population.

Inclusion Criteria:

• Elderly (> 65 years) frail patients undergoing non cardiac surgery under anaesthesia lasting for >60 minutes
• Patient willing and able to complete the requirements of this study.

Exclusion Criteria:

• disabling neuropsychiatric or neurological disorders(including severe dementia, Alzheimer's disease, schizophrenia, severe depression)
• patients suffering from delirium at selection;
• patients who cannot complete the preoperative mental tests (CAM and/or Mini-Mental State Examination (MMSE)) of this clinical trial;

Postoperative inpatients