深低温不改变脑血管压力的自身调节作用
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Static cerebrovascular pressure autoregulation remains intact during deep hypothermia
背景与目的
在深低温状态下婴幼儿脑血流量测定的临床研究已经证明，深低温可降低脑血管压力的自身调节。在同时存在低血压时可得出结论深低温损害脑血管压力的自身调节。我们试图比较了低温和常温处理的仔猪的自身调节下限和自身调节静态率。
方 法
二十只麻醉的新生仔猪（5-7天；10只常温和10只低温20°C）用激光多普勒连续测量皮质红细胞通量，非体外循环诱发失血性低血压。采用分段回归和SRoR，每个主题确定了自身调节下限，每个脑血流自身调节下限确定了上和下限（%改变脑血管阻力/ %改变脑灌注压）。
结 果
自身调节下限是1.4 mm Hg（低温下的仔猪95%CI 为10～14mmHg；P=0.6）。在常温组自身调节中值下限为39mmHg Vs 低温组为35mmHg。自身调节压力的稳态定义为自身调节静态率> 0.5，在所有的常温受试者（自身调节静态率为 0.72 [ 0.65-0.87 ]）和9/10的低温受试者（自身调节静态率为 0.65 [ 0.52-0.87 ]）中有所表现。
结 论
在深低温猪模型中已经证明了脑血管压力的自身调节的稳态。在低温和常温的猪模型中脑血流自动调节下限和自身调节静态率相似。
原始文献摘要
Goswami D,McLeod K，Leonard S,et al.Static cerebrovascular pressure autoregulation remains intact during deep hypothermia.Paediatr Anaesth.2017 Jul 18. doi: 10.1111/pan.13205.
Abstract
Background: Clinical studies measuring cerebral blood flow in infants during deep hypothermia have demonstrated diminished cerebrovascular pressure autoregulation.The coexistence of hypotension in these cohorts confounds the conclusion that deep hypothermia impairs cerebrovascular pressure autoregulation.
Aim: We sought to compare the lower limit of autoregulation and the static rate of autoregulation between normothermic and hypothermic piglets.
Methods: Twenty anesthetized neonatal piglets (5-7 days old; 10 normothermic and 10 hypothermic to 20°C) had continuous measurements of cortical red cell flux using laser Doppler flowmetry, while hemorrhagic hypotension was induced without cardiopulmonary bypass. Lower limit of autoregulation was determined for each subject using piecewise regression and SRoR was determined above and below each lower limit of autoregulation as (%change cerebrovascular resistance/%change cerebral perfusion pressure).
Results: The estimated difference in lower limit of autoregulation was 1.4 mm Hg (lower in the hypothermic piglets; 95% C.I. 10 to 14 mm Hg; P=0.6). The median lower limit of autoregulation in the normothermic group was 39 mm Hg [IQR 38-51] vs 35 mm Hg [31-50] in the hypothermic group. Intact steady-state pressure autoregulation was defined as static rate of autoregulation >0.5 and was demonstrated in all normothermic subjects (static rate of autoregulation=0.72 [0.65-0.87]) and in 9/10 of the hypothermic subjects (static rate of autoregulation=0.65 [0.52-0.87]). This difference in static rate of autoregulation of 0.06 (95% C.I. 0.3 to 0.1) was not significant (P=0.4)
Conclusion: Intact steady-state cerebrovascular pressure autoregulation is demonstrated in a swine model of profound hypothermia. Lower limit of autoregulation and static rate of autoregulation were similar in hypothermic and normothermic subjects.
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