Abstract: Objective To observe the influence of the sub-anesthetic doses of ketamine and dexmedetomidine on early postoperative cognitive dysfunction(POCD) und
erwent orthopedic surgery in elderly patients,and to clarify its related mechanism.
Methods 120 patients aged 60 years underwent elective orthopedic surgery were randomly
divided into ketamine group,dexmedetomidine group,ketamine+dexmedetomidine
group and  control group,30 cases in each group.All patients received total intravenous anesthesia.Before anesthesia,
the patients in ketamine group received 0.5 mg?kg-1 ketamine intravenous injection.The patients in dexmedetomidine group received infusion of dexmedeto
midine 1 μg/kg at first,followed by  0.5 μg/kg/h infusion until 30 min before the end of operation.The patients in ketamine+dexmedetomidine group
received intravenous infusion of ketamine and dextromedetomidine.The patients in control group received intravenous infusion of saline.The Mini Mental State Examination (MMSE) was used to assess cognitive function 1 d before operation and 1,7 d after operation.The incidence of POCD was recorded.Blood samples were taken before anesthesia induction,at the end of operation and 24 h after  operation for
determination of IL-6.  Results Compared with control group,the time from consciousness
 to extubation of the patients in dextromedetomidine group was singnificantly prolonged(P<0.05).
 The incidence of POCD were 26.7% and 13.3% in control group at 1,7 d after operation,6.7% and 0 in ketamine group,
 20.0% and 10.0% in dexmedetomidine group, 13.3% and 3.3% in ketamine+dexmedetomidine group. Compared with  control grou
p,the incidence of POCD  in ketamine group at 1,7 d after operation was significantly decreased (P<0.05),the incidence of POCD in dexmedetomidine group and ketamine + dexmedetomidine group at 1,7 d after operation had no
   significant differences(P> 0.05).The serum IL-6 levels had no significant difference between various groups (P<0.05).
Conclusion The application of sub-anesthetic dose of ketamine can reduce the incidence of early POCD in orthopedic surgery.Dexmedetomidine alone or combined with ketamine can not reduce the incidence of early POCD in orthopedic surgery.The occurrence of POCD has nothing to do
 with inflammatory reaction.
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Key words: postoperative cognitive dysfunction, orthopedic surgery, ketamine, dexmedetomidine, interleukin-6, elderly