Critical Thresholds for Transcranial Doppler Indices of Cerebral Autoregulation in Traumatic Brain Injury
作者：Enrico Sorrentino • Karol P. Budohoski •Magdalena Kasprowicz • Peter Smielewski •Basil Matta • John D. Pickard • Marek Czosnyka
摘自：Neurocrit Care (2011) 14:188–193
经颅多普勒衍生的脑自动调节指数与TBI患者预后有重要关联。 我们回顾性分析了患者数据材料，以确定对这些指数的对预后结果进行判别的阈值。
方法：248名颅脑损伤后的镇静和通气患者数据被选入该研究。用于评估自动调节的指数为Mx（血流速度与脑灌注压相关系数）或Mxa（血流速度与动脉血压相关系数）。 根据存活 - 死亡（有利 - 不利结果）和Mx和Mxa的变化阈值，创建2×2个表格。 我们计算了皮尔逊的卡方。在生存 - 死亡（有利 - 不利结果）之间返回最高卡方值的Mx或Mxa值被认为具有最佳判别性的阈值。
结论：Mx和Mxa证明较差的自动调节与较差的结果和较高的死亡率相关（Mx为P = 0.0033，Mxa为P = 0.047）。 这两个指数对预测有利结果比死亡率更有效。 Mx的卡方显示双峰，阈值为0.05和0.3。 Mxa只有一个峰值为0.3。 Mx的峰值卡方（11.3）大于Mxa（8.7），表明Mx是比Mxa更好的判别指数。
讨论：我们认为Mx大于0.3表示明确受损的自动调节并且低于0.05良好自动调节。 对于0.05和0.3之间的值，自动调节的状态是不确定的。由经颅多普勒测量的脑血流信号计算的自动调节指数Mx和Mxa似乎都具有预测价值，尤其是针对有利结果的预测。对较大样本人群的研究将阐明这些阈值是否适用于所有患者或仅适用于其中一部分患者。
Abstract
Background Transcranial Doppler-derived indices of cerebral autoregulation are related to outcome after TBI.
We analyzed our retrospective material to identify thresholds discriminative of outcome for these indices.Methods 248 sedated and ventilated patients after head injury were eligible for the study. The indices of autoregulation derived from transcranial Doppler were calculated as correlation coefficients of blood flow velocity with cerebral perfusion pressure (index Mx) or arterial blood pressure (index Mxa). 2 9 2 tables were created grouping patients according to survival–death or favorable–unfavorable outcomes and varying thresholds for Mx and Mxa.Pearson’s chi-square was calculated. Thresholds returning the highest chi-square value were assumed to have the best discriminative value between survival–death and favorable–unfavorable outcomes.
Results Mx and Mxa demonstrated that worse autoregulation is associated with poorer outcome and greater mortality (P = 0.0033 for Mx and P = 0.047 for Mxa).
Both indices were more effective for prediction of favorable outcome than mortality. Chi-square for Mx showed a double peak with thresholds at 0.05 and 0.3. Mxa had only one peak at 0.3. Peak chi-square for Mx (11.3) was greater than for Mxa (8.7), indicating that Mx was a better discriminant of outcome than Mxa.
Conclusions We propose that Mx greater than 0.3 indicates definitely disturbed autoregulation and lower than 0.05 good autoregulation. For values between 0.05 and 0.3 the state of autoregulation is uncertain.
Introduction
The importance of the measurement of cerebral autoregulation has been highlighted in many studies over the past decades [1–3]. Continuous monitoring seems to be important as autoregulation status may change dynamically— e.g., during plateau waves of intracranial pressure (ICP) [4], incidental arterial hypotension [5], vasospasm,hyperemia [6], or refractory intracranial hypertension [7]. The mean flow velocity index (Mx) is a correlaion coefficient between slow fluctuations (whose average period ranges from 20 s to 3 min) of flow velocity (FV) in the middle cerebral artery (MCA), measured through TCD,and global cerebral perfusion pressure (CPP). It has been postulated that when there is a direct relationship between these two factors (index is positive), the cerebrovascular autoregulation is impaired [8]. Zero or negative index signifies intact autoregulation. Mxa is a similar index,derived from the correlation between FV and mean arterial
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