A majority of the elderly patients undergo surgery for malignant tumors. For these patients, postoperative tumor recurrence and metastasis are main factors that worsen long-term outcomes. The investigators hypothesize that dexmedetomidine supplemented analgesia in elderly patients after cancer surgery may help to maintain immune function and improve long-term outcomes, possibly by relieving stress and inflammatory response, improving analgesic efficacy and sleep quality, and reducing delirium incidence.

A majority of the elderly patients undergo surgery for malignant tumors. For these patients, postoperative tumor recurrence and metastasis are main factors that worsen the quality of life and shorten the duration of survival. Perioperative immune function is a key element that influences postoperative tumor recurrence and metastasis; but it is subject to the impacts of many factors. Studies showed that elevated cortisol level and inflammation provoked by surgical stress result in suppression of immune function, whereas dexmedetomidine alleviates the elevated cortisol level and inhibit excessive inflammation; high-dose opioids inhibit the immune function and increase the invasiveness of tumor cells, whereas dexmedetomidine reduces the consumption of opioids during perioperative period; postoperative sleep disturbances also impair immune function, whereas dexmedetomidine improves sleep quality in patients after surgery; occurrence of postoperative delirium is associated with increased mortality, whereas dexmedetomidine reduces delirium incidence. The investigators hypothesize that dexmedetomidine supplemented analgesia in elderly patients after cancer surgery may improve the long-term outcomes, possibly by relieving stress and inflammatory response, improving analgesic efficacy and sleep quality, and reducing delirium incidence.

Inclusion Criteria:

• Age >= 65 years, < 90 years;
• Scheduled to undergo curative resection for primary solid organ cancer under general anesthesia, with an expected duration of surgery >=2 hours;
• Planned to use patient-controlled intravenous analgesia after surgery;
• Provide written informed consent.

Exclusion Criteria:

• Preoperative history of schizophrenia, epilepsy, parkinsonism or myasthenia gravis;
• Preoperative radio- or chemotherapy;
• Inability to communicate in the preoperative period because of coma, profound dementia or language barrier;
• Preoperative obstructive sleep apnea (previously diagnosed as obstructive sleep apnea, or a STOP-Bang score >= 3 and serum HCO3- >= 28 mmol/L);
• Brain trauma or neurosurgery;
• Preoperative left ventricular ejection fraction < 30%, sick sinus syndrome, severe sinus bradycardia (< 50 beats per minute), or second-degree or above atrioventricular block without pacemaker;
• Severe hepatic dysfunction (Child-Pugh class C) or severe renal dysfunction (requirement of renal replacement therapy before surgery);
• ASA classification >= IV.