ABSTRACT
Objective To determine the median effective target plasma concentration (EC50) of propofol inhibiting the response to laryngeal mask airway (LMA) insertion when combined with dexmedetomidine.Methods ASA Ⅰ or Ⅱ patients of both sexes,aged 20-60 yr,with body mass index 20-25 kg/m2,scheduled for surgeries under general anesthesia,were studied.EC50 of propofol was determined by modified Dixon' s up-and-down sequential experiment.After dexmedetomidine 1.0 μg/kg was infused over 10 min,propofol was infused by targetcontrolled infusion.The initial target plasma concentration of propofol was set at 3.0 μg/ml.LMA was inserted when the target effect-site concentration of propofol and target plasma concentration of propofol reached the balance and BIS value was 50-60.Each time the target concentration increased/decreased by 0.2 μg/ml according to the occurrence of the response to LMA insertion.The response to LMA insertion was defined as the occurrence of coughing,body movement,laryngospasm or systemic voluntary movement.EC50 and 95 ％ confidence interval (CI)of propofol for inhibition of the response to LMA insertion were calculated.Results The EC50 of propofol required for inhibition of the response to LMA insertion was 2.351 (95％ Cl 1.737-2.600) μg/ml when combined with dexmedetomidine 1.0 μg/kg.Conclusion The EC50 of propofol inhibiting the response to LMA insertion is 2.351 μg/ml when combined with dexmedetomidine.