Effects of dexmedetomidine on the incidence of postoperative delirium in critically ill elderly patients

INTERVENTION: B:General anesthesia will be induced and maintained during surgery. Patient controlled analgesia will be provided for postoperative analgesia whenever necessary. Sedation level will be assessed with Richmond Agitation Sedation Scale (RASS) hourly after ICU admission. Study drug will be started when the RASS score is ‐2 or above. Normal saline will be administered by intravenous infusion at a rate of 0.025 ml/kg/h until 8:00 am on the first day after surgery. ;Dexmedetomidine group :General anesthesia will be provided during surgery and patient‐controlled analgesia will be provided for postoperative analgesia in the same way as those in the placebo group. Sedation level will be assessed with Richmond Agitation Sedation Scale (RASS) hourly after ICU admission. Study drug will be started when the RASS score is ‐2 or above. Dexmedetomidine will be administered by intravenous infusion at a rate of 0.025 ml/kg/h (0.1 ug/kg/h) until 8:00 am on the first day after surgery. ; CONDITION: postoperative delirium in critically ill elderly patients PRIMARY OUTCOME: Incidence of postoperative delirium within the first seven days after surgery; SECONDARY OUTCOME: Postoperative all cause 30‐day mortality;Incidence of postoperative non‐delirium complications (during hospitalization or until 30 days after surgery);Duration of mechanical ventilation, length of stay in the ICU and hospital after surgery; INCLUSION CRITERIA: 1. Elderly patients (age >=65 years); 2. Planning to undergo elective noncardiac surgery under general anesthesia; 3. Admitted to ICU after surgery before 8:00 pm.