Abstract: Objective To investigate the effects of dexmedetomidine on effect-site concentration of remifentanil for successful laryngeal mask (LMA) insertion in women and to provide clinical basis in the application of dexmedetomidine to general anesthesia retaining spontaneous respirations. Methods Forty-eight patients scheduled for hysteroscopic examinations were randomly allocated to experiment group (group D) and control group (group P).At the beginning of anesthesia induction,experimental drugs (dexmedetomidine 0.5 μg/kg in group D;normal saline in group P) were intravenously administrated at a constant velocity for 10 min by an infusion pump in each group.Propofol was effect-site target controlled infused following saline and dexmedetomidine administration completion.Three minutes after propofol infusion,remifentanil was effect-site target controlled infused and the initial concentration was set at 2.0 μg/ml in both groups.The status of LMA insertion was recorded,and according to the recorded status,the target remifentanil concentration of the following patient was determined by Dixon's up-and-down method (ratio is 1:0.85),and then EC₅₀ of remifentanil was determined.The respiratory and circulatory parameters at each stage (T0:before applying dexmedetomidine or saline;T1:3 min after applying dexmedetomidine or saline;T2:after TCI of remifentanil and before LMA insertion;T3:1 min after LMA insertion;T4:5 min after LMA insertion) were recorded and compared. Results Effect-site EC₅₀ values of remifentanil for successful LMA insertion were 2.74 μg/ml (95%CI:2.30-3.36 μg/ml) for group D and 1.13 μg/ml (95%CI:0.91-1.38 μg/ml) for group P (P<0.05).After TCI of remifentanil,SBP in group P was significantly lower than that in group D (T2,P=0;T4,P=0.002);HR in group D was significantly lower than that in group P at T1,T3,T4 after dexmedetomidine was administered (T1,T3,T4,P=0).The incidence of apnea in group D was significantly lower than that in group P whether before (36.36% vs.76.92%,P=0.003) or after (16.67% vs.66.67%,P=0.018) LMA insertion. Conclusion Dexmedetomidine can significantly reduce the EC₅₀ values of remifentanil for successful LMA insertion,and beneficial to preserve spontaneous respiration in general anesthesia with LMA airway,worthy of clinical application.