The goal of this clinical trial is to learn how postoperative infusion of dexmedetomidine would influence postoperative delirium in elderly patients undergoing lung surgery. The main questions it aims to answer are :

1. Does postoperative dexmedetomidine reduce the incidence of delirium after lung surgery?
2. Does postoperative dexmedetomidine introduce other medical problems? Researchers will compare dexmedetomidine and sufentanil to see if dexmedetomidine works to reduce delirium.

Participants will undergo routine postoperative care:

1. Patient-controlled self anesthesia with sufentanil only or combination of sufentanil and dexmedetomidine
2. Postoperative visit twice a day for at least seven days

Inclusion Criteria:

• elective surgery for lobectomy or segmentectomy

Exclusion Criteria:

• local allergy to anesthetics;
• patients with a clear preoperative history of nervous system and mental system diseases or long-term use of sedatives or antidepressants;
• history of alcoholism, drug abuse or drug dependence;
• have a history of brain surgery or injury;
• epilepsy and associated mental and cognitive dysfunction, long-term stress stimulation, or psychological disorders;
• sick sinus syndrome, second-degree or greater atrioventricular block or other contraindications for use of α2 adrenergic agonist;
• liver and kidney insufficiency.