Delirium is defined as an acute onset and fluctuating course of mental status change with inattention and an altered level of consciousness. Delirium in the postoperative period can be divided into emergence delirium and postoperative delirium, based on the time of onset (Silverstein et al., 2007).Postanaesthesia delirium is a frequent and potentially serious problem affecting the safety of patients and medical personnel. Clinical studies demonstrated that postoperative delirium is associated with worse outcomes such as prolonged hospital stay, postdischarge institutionalization, and increased mortality (Ely et al., 2004a; Thomason et al., 2005; Robinson et al., 2009). Multiple factors may contribute to the development of postoperative delirium, including patient's medical condition, administration of anesthetics or analgesics and degree of operative stress (Yildizeli et al., 2005; Robinson & Eiseman, 2008; Deiner & Silverstein, 2009). Sevoflurane anesthesia have been reported to be associated with more emergence delirium in pediatric patients, when compared with propofol anesthesia. It is not clear if propofol anesthesia will benefit the geriatric patients on postoperative delirium, when compared with sevoflurane anesthesia. We hypothesize that propofol anesthesia will reduce the rate of postoperative delirium by 50% when compared with sevoflurane anesthesia.

Inclusion Criteria:

• American Society of Anesthesiologists Physical Status classification (ASA_PS) class I-III
• Aged 60 years or above
• Elective major surgery under general anesthesia

Exclusion Criteria:

• ASA_PS>=IV
• Aged under 60 yr old
• Body mass index (BMI) >30
• Neurologic disease
• Cardiac surgery and neurologic surgery
• Anticonvulsant drugs
• Chronic analgesics intake
• Participating in the investigation of another study