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Objective: The aim of this study was to determine the target plasma concentration of remifentanil TCI for tracheal intubation in 50% of patients (CP50) with 1.3MAC sevoflurane inhalated .Methods: Thirty-two patients, ASA physical statusⅠorⅡof both sexes aged 18-59 years old, scheduled to undergo elective surgery, were enrolled in this study. During 1.3MAC sevoflurane tidal breathing induction, a predetermined dose of reminfentanil was infused at an effect-site concentration using a TCI infusion pump （Minto pharmacokinetics model for reminfentanil）. When the patients lost consciousness, 0.6mg/kg doses of rocuronium was injected to facilitate tracheal intubation. The target effect-site concentration of reminfentanil applied for each patients was determined by the response of the previously tested one, using a modified Dixon-Mood’s up-and-down method. The initial target effect-site concentration was 3.0 ng/ml, and the change step of doses was 0.5 ng/ml. Intubating conditions were evaluated according to T. Fuchs-Buder Scoring System. Successful intubation was defined as excellent or good intubation conditions, while failure as poor conditions. Mean arterial pressure （MAP）, heart rate （HR） were recorded at before anaesthetic induction （baseline values, T0）, 1 min before（ T1） and after（ T2） intubation, also 2 min after （T3） induction. The up-and-down data were processed by a probit analysis, which enabled us to derive the Cp50, Cp95 with 95% confidence intervals（95% CI）. And dose-response curve was from logistic regression.Results: Compared with baseline values, MAP and HR of 1min before intubation were decreased significantly （P<0.05）, while there were no significant decreasing after 1 and 2min after intubation （P>0.05）. From probit analysis, CP50 and Cp95 of remifentanil TCI were 4.40ng/ml (95% confidence intervals 4.07-4.78 ng.ml-1 ) and 5.34ng.ml-1 (95% confidence intervals 4.87-8.22 ng.ml-1 ), respectively, and deriving dose-response curve from logistic regression.Conclusion: The target plasma concentration of remifentanil TCI for successful tracheal intubation in 50% of patients (CP50) was 4.40ng/ml, 95%CI （4.07, 4.78）ng.ml-1, during inhalational induction with 1.3MAC sevoflurane .
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