Effects of remifentanil infused at different rates on median effective target plasma concentration of propofol inhibiting responses to laryngeal mask airway insertion in pediatric patients

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Objective To compare the effects of remifentanil infused at different rates on median effective target plasma concentration (EC50) of propofol inhibiting responses to laryngeal mask airway (LMA) insertion and determine the optimum infusion rate of remifentanil when used for fiberoptic bronchoscopy in pediatric patients.Methods Eighty-four ASA Ⅰ or Ⅱ pediatric patients,aged 7 months-3 years,scheduled for elective fiberoptic bronchoscopy,were randomly assigned into 3 groups (n =28 each):normal saline group (group C),remifentanil infused at 3 ng· kg-1 ·min-1 group (group R1) and remifentanil infused at 5 ng· kg-1 · min-1 group (group R2).Responses to LMA insertion were defined as body movement and/or bucking during insertion.The initial target plasma concentrations of propofol were 5.2,4.8 and 4.4 μg/ml in groups C,R1 and R2,respectively.The target plasma concentration of propofol was determined by up-and-down sequential allocation.Each time the target plasma concentration increased/decreased by 0.2μg/ml.EC50 and 95 ％ confidence interval of propofol blunting responses to LMA insertion were determined by probit method.Results EC50 (95 ％ confidence interval) of propofol was 5.03 (4.92-5.12) μg/ml,4.71 (4.58-4.84) μg/rnl and 4.46 (4.20-4.94) μg/ml in groups C,R1 and R2,respectively.There was no significant difference in EC50 of propofol between groups R1 and C (P ＞ 0.05).EC50 of propofol was significantly lower in group R2 than in groups C and R1 (P ＜ 0.05).Conclusion The infusion rate of remifentanil should not be lower than 5 ng· kg-1· min-1 when combined with propofol in pediatric patients undergoing fiberoptic bronchoscopy. Key words: Piperidines; Infusions, intravenous; Propofol; Dose-response relationship, drug; Child ; Anesthesia, general; Bronchoscopy