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.

Objective To determine the effectiveness of preoperative sedation with rectal midazolam and atropine alone or combined with ketamine in infants and young children.Methods One-hundred and six ASA Ⅰ or Ⅱ infants and young children aged 2 months-2 years scheduled for elective general surgical operation were studied in a double blind fashion.The patients were randomly divided into 3 groups:group M received rectal atropine 0.02 mg?kg~(-1) and midazolam 0.5 mg?kg~(-1)(n=39);group MK and MKK received rectal atropine 0.02 mg?kg~(-1), midazolam 0.5 mg?kg~(-1) and ketamine 4 mg?kg~(-1)(MK,n=34)or 8 mg?kg~(-1)(MKK,n=33).The patients were transferred from the ward to the operating room(OR)30 min after rectal administration.Depth of sedation was evaluated before and 15 min after rectal administration; when the patients were separated from their parents and on arrival in OR using De Jong's sedation score system.SpO_2 and HR were monitored in OR.Results The patients were better sedated in group MK and MKK than in group M after rectal administration.Significantly more patients were asleep on seperation from their parents and on arrival in OR in group MK and MKK than in group M. Significantly more patients were calm and not crying at venepuncture in group MKK(63%)and group MK(32%) than in group M(18%).Conclusion Rectal midazolam combined with ketamine and atropine results in better preoperative sedation than rectal midazolam alone in infants and young children.