Delirium, an acute change in mental status, is a serious medical complication among hospitalized patients. Syndrome of delirium involves agitation, sleep disturbance, affective disorders and cognitive disruptions.

One vulnerable period for developing delirium is in the postoperative days. Postoperative delirium often initiates a cascade of adverse consequences including an increase in length of stay and hospital costs, and greater mortality. The investigators have observed that the incidence of postoperative delirium in patients after renal transplantation is about 20-30% in our hospital.

Several studies have revealed that dexmedetomidine, as a widely used sedative during anesthesia, can decrease the incidence of postoperative delirium after cardiac surgery. The investigators aim to examine whether administration of dexmedetomidine can reduce postoperative delirium after living donor renal transplantation in adult patients.

Inclusion Criteria:

• age > 17 and < 60 years;
• American Society of Anesthesiology (ASA) I-III;
• admitted for living donor renal transplantation.

Exclusion Criteria:

• Patients with a history of drug abuse;
• preoperative history of schizophrenia, epilepsy, parkinsonism, use of cholinesterase inhibitor, inability to communicate in the preoperative period (coma, profound dementia, or language barrier).