Effect of different doses of dexmedetomidine on median effective concentration of propofol required to prevent response to Supreme laryngeal mask airway insertion in aged patients

Objective To investigate the effect of different doses of dexmedetomidine on the median effective concentration (EC50) of propofol required to prevent the response to Supreme laryngeal mask airway (LMA) insertion in aged patients.Methods ASA Ⅰ or Ⅱ patients of both sexes,aged ≥ 65 yr,with a body mass index of 20-28 kg/m2,undergoing knee operation under general anesthesia,were randomly divided into 3 groups:control group (group C),small dose dexmedetomidine group (group D1 ) and large dose dexmedetomidine group (group D2 ).Dexmedetomidine 0.4 and 0.8 μg/kg were infused intravenously over 10 min in groups D1 and D2 respectively,while group C received the equal volume of normal saline instead.Anesthesia was induced with target-controlled infusion of propofol.The initial target plasma concentration of propofol was set at 3.5,3.0 and 2.6 μg/ml in groups C,D1 and D2 respectively.Following equilibration between the plasma and effect-site concentration of propofol,LMA was inserted when BIS value was 50-60.EC50 was determined by up-and-down sequential trial.The target plasma concentration of propofol increased/decreased by 10％ in the next patient depending on whether or not the LMA insertion response occurred.Positive LMA insertion response was defined as body movement,comer of the mouth movement,biting LMA,bucking and/or wallowing during insertion.The EC50 and 95％ confidence interval (CI) of propofol required to prevent LMA insertion response were calculated with sequential method.Results EC50(95％ CI) of propofol was 3.57 μg/ml (2.91-3.87 μg/ml),3.09 μg/ml (2.66-3.53 μg/ml) and 2.62 μg/ml (2.30-3.15 μg/ml) in groups C,D1 and D2 respectively.EC50 was significantly lower in groups D1 and D2 than in group C,and in group D2 than in group D1 ( P ＜ 0.05 ).Conclusion Dexmedetomidine 0.4 and 0.8 μg/kg infused intravenously can reduce the EC50 of propofol required to prevent the response to Supreme LMA insertion in aged patients,and the effect of 0.8 μg/kg is more obvious. Key words: Dexmedetomidine; Propofol; Dose- response relationship, drug; Laryngeal masks; Aged