Effects of different doses of dexmedetomidine on median effective end-tidal concentration of sevoflurane inhibiting responses to tracheal intubation in pediatric patients

Abstract

Objective To evaluate the effects of different doses of dexmedetomidine on median effective end-tidal concentration of sevoflurane (EC50) inhibiting responses to tracheal intubation in pediatric patients.Methods Sixty-seven ASA physical status Ⅰ or Ⅱ patients,aged 3-8 yr,with body weight not exceeding 150％ of the ideal weight,scheduled for elective surgery under general anesthesia,were randomly divided into 3 groups using a random number table:control group (group C,n =22) and different doses of dexmedetomidine groups (group D1,n =23 ; group D2,n =22).Before induction of anesthesia,dexmedetomidine 1.0 and 2.0 μg/kg was infused intravenously over 10 min followed by infusion at a rate of 0.5 and 1.0 μg·kg-1 ·h-1 in D1 and D2 groups,respectively.Anesthesia was induced with inhalation of 5 ％ sevoflurane.After eyelash reflex disappeared,the end-tidal sevoflurane concentration was adjusted to achieve the target concentration and maintained at this level for 15 min.Tracheal intubation was then performed and the response to intubation was scored.The initial end-tidal sevoflurane concentration was 3.5％,2.5％ and 1.5％ in C,D1 and D2 groups,respectively.Up-and-down sequential trial was used to determine the EC50.Each time the concentration of sevoflurane increased/decreased in the next patient depending on whether or not the response to intubation was positive.The positive response to intubation was defined as intubation score ＞ 1.The ratio of concentrations between the two consecutive patients was 1.2.The EC50 and 95％ confidence interval of sevoflurane were calculated.The development of adverse cardiovascular events was recorded after dexmedetomidine administration.Results The adverse cardiovascular events were not observed in D1 group.The incidence of hypotension and brachycardia was 14％ and 9％ in D2 group.The EC50 (95％ confidence interval) of sevoflurane was 3.54％ (3.39％-3.69％),2.37％ (2.24％-2.46％) and 1.41 ％ (1.37％-1.46 ％) in C,D1 and D2 groups,respectively.Compared with group C,the EC50 of sevoflurane was significantly decreased in D1 and D2 groups (P ＜ 0.01).Compared with group D1,the EC50 of sevoflurane was significantly decreased in group D2 (P ＜ 0.01).Conclusion The optimum dose of dexmedetomidine is 1.0 μg/kg (loading dose) and 0.5 μg· kg-1 · h-1 (maintenance dose) when combined with sevoflurane for induction of anesthesia in pediatric patients. Key words: Dexmedetomidine; Anesthesia, inhalation; Intubation, intratracheal; Dose-response relationship, drug; Child