Effects of gender on median effective target plasma concentration of propofol inhibiting responses to laryngeal mask airway insertion

Objective To evaluate the effects of gender on the median effective target plasma concentration (EC50) of propofol inhibiting responses to laryngeal mask airway (LMA) insertion in patients.Methods Fiftyfive ASA physical status Ⅰ or Ⅱ patients,aged 20-60 yr,with body mass index 18-25 kg/m2,requiring LAM insertion,undergoing elective surgery,were divided into 2 groups according to the gender:male group (group M,n =27) and female group (group F,n =28).Propofol was given by target-controlled infusion.Anesthesia was induced with target-controlled infusion of propofol.The concentration of propofol was determined by using modified Dixon's up-and-down method.The initial target plasma concentration of propofol was 3.0 μg/ml (group M) or 2.7μg/ml (group F) and the ratio between the 2 successive concentrations was 1.1.Fentanyl 1 μg/kg was injected intravenously at about 10 min of propofol target-controlled infusion.LMA was inserted after the effect-site and plasma concentrations were balanced.The positive response to LMA insertion was defined as development of swallowing,coughing,biting LMA,body movement and laryngospasm during insertion.When the response to LMA insertion was positive,the concentration of propofol was increased in the next patient and when the response was negative,the concentration was decreased in the next patient.The EC50 and 95 ％ confidence interval of propofol inhibiting responses to LMA insertion were calculated.Results The EC50 (95 ％ confidence interval) of propofol was 3.11 (2.92-3.30) μg/ml in group F and 2.70 (2.55-2.85) μg/ml in group M (/ ＜ 0.05).Conclusion The EC50 of propofol inhibiting responses to LMA insertion is higher in female patients than in male patients. Key words: Sex factors;  Propofol;  Laryngeal masks;  Drug delivery systems;  Dose-response relationship, drug