Abstract: Objective  To investigate the incidence of postoperative delirium after using dexmedetomidine and sub-anesthetic dose of ketamine and to clarify their influence in the incidence of postoperative delirium in elderly orthopedic patients under total intravenous anesthesia.
Methods  One hundred and twenty elderly patients aged more than 60 years underwent elective orthopedic surgery,ASA
Ⅰ-Ⅲ,were randomly divided into 4 groups(n=30): normal saline (control group),ketamine group,dexmedetomidine group,ketamine+dexmedetomidine group.The patients in ketamine group received an intravenous injection of ketamine  at a dosage of 0.5 mg?kg-1.In dexmedetomidine group the patients received dexmedetomidine at a dosage of 1  μg?kg-1 by intravenous injection  before induction of anesthesia followed by a continuous infusion at0.5  μg/kg/h till 30 min before the end of operation.In ketamine+dexmedetomidine group,the patients received both 0.5 mg?kg-1 ketamine  and  1.0  μg/kg dexmedetomidine over 10 min by  introvenous injection followed by a continuous infusion of dexmedetomidine at 0.5 μg/kg/h till 30 min before the end of operation. The patients in control group were administered with the same amount of normal saline.The blood sample
s were taken before anesthesia,at the end of operation and 24 h after operation.The level of serum interleukin-6 (IL-6) was detected using enzyme-linkedim
munosorbent assay (ELISA).The Confusion Assessment Method (CAM) was applied to evaluate postoperative delirium 1 h,1 d and 3 d after operation.
Results  There were no statistical significance in age,gender,weight,operation time,anesthesia time,anesthesia dosage,bleeding,urine volume and infusion of the patients between four groups(P>0.05).13 patients in the study developed delirium：8 patients in ketamine group (26.7%),2 patients in dexmedetomidine group (6.7%),3 patients in control group (10%);no delirium was found in ketamine+dexmedetomidine group. Compared with control group,the incidence rate of delirium in ketamine group was increased significantly (P<0.05).Compared with ketamine group,
the incidence rate of delirium in ketamine+dexmedetomidine group was decreased significantly (P<0.05).There was no significant difference in serumIL
-6 levels of patients between four groups(P>0.05).
Conclusion When they are applied together,dexmedetomidine could alleviate the side effects of ketamine and could decrease the incidence rate of delirium which mechanism is not responsible with inflammation.

Key words: dexmedetomidine, ketamine, interleukin-6, anesthesia,general, postoperative delirium, elderly