Postoperative delirium（POD）is a common complication that can directly affect important clinical outcomes, and exert an enormous burden on patients, their families, hospitals, and public resources. In order to evaluate whether an intraoperative administration of low-dose neuroleptanalgesia reduces postoperative delirium, droperidol 1.25 mg and fentanyl 0.025 mg or normal saline is used by intravenous injection 30 minutes before the end of the operation, in elderly patients with non-cardiac major surgery under general anesthesia. The efficiency and safety of neuroleptanalgesia on the incidence of POD would be evaluated in elderly patients.

Inclusion Criteria:

1. Age ≥ 65 years old and ≤ 85 years old;
2. Selective non-cardiac major surgery;
3. Informed consent and voluntary participation in the trial;
4. ASA class I-II;
5. Anticipated operation duration ≥ 2 hours;
6. No plan to ICU after operation.

Exclusion Criteria:

1. Neurosurgery;
2. Patients with neurological and mental diseases: such as basal ganglia disease, Parkinson's syndrome, severe central nervous depression, Alzheimer's disease , etc;
3. Patients with prolonged Q-T interval, cardiac repolarization disorder and other severe arrhythmia;
4. Patients with severe cardiopulmonary disease, liver and kidney dysfunction;
5. Allergic or contraindications to droperidol or fentanyl citrate;
6. Admitted to ICU after operation.
7. Operation duration < 2 hours;