探讨不同剂量的右美托咪定（Dex）对七氟烷抑制50%患儿切皮诱发肾上腺素能反应的最低肺泡有效浓度（MAC_BAR）的影响。

择期拟行下腹部手术患儿81例，年龄2~6岁，ASA Ⅰ或Ⅱ级，随机分为3组，D₀组（负荷量、维持量均为0.9%氯化钠液）27例，D_0.5组（负荷量0.5 μg/kg、维持量0.5 μg·kg^-1·h^-1）27例，D₁组（负荷量1 μg/kg、维持量1 μg·kg^-1·h^-1）27例。在麻醉诱导前15 min开始输注Dex，气管插管后各组初始的七氟烷呼气末浓度均为4%，按改良序贯法进行试验，以切皮后5 min内MAP或HR升高幅度≥切皮前15%为阳性反应，计算七氟烷MAC_BAR及其95%置信区间。

3组间比较差异有统计学意义（P<0.01）。D_0-1组MAC_BAR分别为（3.95±0.1）%（95% CI=3.88%~4.02%）、（3.05±0.1）%（95% CI=2.98%~3.12%）、（1.90±0.0）%（95% CI=1.90%~1.90%）。D_0.5组、D₁组的七氟烷MAC_BAR较D₀组分别降低了23%、52%，差异有统计学意义（P<0.01）。

负荷量0.5 μg/kg、维持量0.5 μg·kg^-1·h^-1的Dex可降低行下腹部手术小儿七氟烷MAC_BAR 23%，当Dex剂量增加一倍时，可降低MAC_BAR约52%。

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 (MAC_BAR).

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 MAC_BAR of sevoflurane and its 95% confidence interval were calculated.

The differences in the three groups were significant (P<0.01). The MAC_BAR 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 D_0.5, and (1.90±0.0)% (95% CI=1.90%-1.90%) in group D₁. The MAC_BAR reduction of sevoflurane was 23% in group D_0.5 and 52% in group D₁ (P<0.01).

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 MAC_BAR 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 MAC_BAR values of sevoflurane.