A recent study of the investigators showed that, in elderly patients who were admitted to the ICU after surgery and did not require mechanical ventilation, low-dose dexmedetomidine infusion (at a rate of 0.1 ug/kg/h, for 15 hours) prolonged the total sleep time, increased the percentage of N2 sleep (and reduced the percentage of N1 sleep), increased the efficiency of sleep and improved the subjective sleep quality. Another study of the investigators showed that low-dose dexmedetomidine infusion in elderly patients who were admitted to the ICU after non-cardiac surgery improved the subjective sleep quality and reduced the daily prevalences of delirium during the first 3 days after surgery. We hypothesize that dexmedetomidine supplemented analgesia can improve the structure and circadian rhythm of sleep, and reduce the incidence of delirium in elderly patients after major non-cardiac surgery.