Effects of different doses of dexmedetomidine on MACBAR of sevoflurane in children

Objective To observe the effect of different doses of dexmedetomidine (Dex) on the minimum alveolar concentration of sevoflurane to blockade adrenergic response to surgical incision in 50% of children (MACBAR). Methods Eighty-one children, 2-6 years old, with ASAⅠ or Ⅱ undergoing lower abdominal surgery, were randomly allocated into three groups, receiving saline only (27 cases) or a bolus dose of 0.5 μg/kg and maintenance dose of 0.5 μg·kg-1·h-1 Dex (27 cases) or a bolus dose of 1 μg/kg and maintenance dose of 1 μg·kg-1·h-1 Dex (27 cases) before induction. The initial concentration of sevoflurane was 4% for each group after intubation. The "modified up-and-down" method (Sympathetic responses to surgical incision was considered positive if the MAP or HR increased≥15%) was used, and the MACBAR of sevoflurane and its 95% confidence interval were calculated. Results The differences in the three groups were significant (P<0.01). The MACBAR of sevoflurane was respectively (3.95±0.1)% (95%CI=3.88%-4.02%) in group D0, (3.05±0.1)% (95% CI=2.98%-3.12%) in group D0.5, and (1.90±0.0)% (95% CI=1.90%-1.90%) in group D1. The MACBAR reduction of sevoflurane was 23% in group D0.5 and 52% in group D1 (P<0.01). Conclusions A bolus dose of 0.5 μg/kg and maintenance dose of 0.5 μg·kg-1·h-1 dexmedetomidine results in a 23% decrease in the MACBAR of sevoflurane. Increasing the dose of dexmedetomidine to 1 μg/kg and 1 μg·kg-1·h-1 produces a further 29% decrease in the MACBAR values of sevoflurane. Key words: Pediatrics; Sevoflurane; Dexmedetomidine; Minimum alveolar concentration