体外循环中脑血流自主调节限度的预测

背景在体外循环（ cardiopulmonary bypass, CPB ）时，平均动脉压（ mean arterial blood pressure, MAP）的目标值是根据经验确定的。我们先前已经阐述过，近红外光谱仪（near-infiared spectroscopy, NIRS）监测脑氧饱和度可用于临床监测脑血流的自主调节。本研究假设CPB过程中，通过自动调节下限（1imit of autoregulation，LLA）确定MAP时，使用近红外光谱的方法比根据年龄、术前病史、术前血压为基础决定的经验性MAP更准确。方法对232例体外循环行冠状动脉搭桥术和（或）动脉瓣手术的患者使用多普勒和近红外光谱监测大脑中动脉血流。计算MAP和脑血流速度（平均速度指数）、MAP和近红外光谱数据（脑血氧饱和度指数）之间连续动态的皮尔逊相关系数。当自主调节存在时，脑血流和MAP之间没有相关性（平均流速与氧饱和度系数接近0），当MAP低于LLA时，平均流速与氧饱和的系数接近1。LLA定义为随着MAP不断下降，平均流速指数升高超过0．4时的MAP。通过线性回归评估手术前收缩压、MAP、低于基线10％的MAP和LLA时的平均氧饱和度指数之间的关系。结果在观测到LLA的225例患者中，LLA时的MAP为66mmHg（95％C143—93mmHg）。经过年龄、性别、卒中史、糖尿病、高血压等因素矫正后，术前MAP与UA之间没有相关性，但是脑血氧饱和度指数〉0．5与LLA相关。LLA在219例患者可以通过脑血氧饱和度指数来确定。平均流速指数与脑血氧饱和度指数的LLA平均差为-0．2±10．2mmHg。术前收缩压与较高的LLA相关，但是仅限于术前收缩压≤160mmHg者。结论CPB期间，LLA时患者的MAP范围很大，难于对此进行估计。脑血氧饱和度指数实时监测自动调节可提供一个更合理的手段来实现CPB期间的个性化MAP。

BACKGROUND： Mean arterial blood pressure （MAP） targets are empirically chosen during cardiopulmonary bypass （CPB）. We have previously shown that near-infrared spectroscopy （NIRS） can be used clinically for monitoring cerebral blood flow autoregulation. The hypothesis of this study was that real-time autoregulation monitoring using NIRS-based methods is more accurate for delineating the MAP at the lower limit of autoregulation （LLA） during CPB than empiric determinations based on age, preoperative history, and preoperative blood pressure. METHODS： Two hundred thirty-two patients undergoing coronary artery bypass graft and/or valve surgery with CPB underwent transcranial Doppler monitoring of the middle cerebral arteries and NIRS monitoring. A continuous, moving Pearson correlation coefficient was calculated between MAP and cerebral blood flow velocity and between MAP and NIRS data to generate mean velocity index and cerebral oximeter index. When autoregulated, there is no correlation between cerebral blood flow and MAP （i. e., mean velocity and cerebral oximetry indices approach 0）; when MAP is below the LLA, mean velocity and cerebral oximetry indices approach 1. The LLA was defined as the MAP at which mean velocity index increased with dedining MAP to 90. 4. Linear regression was performed to assess the relation between preoperative systolic blood pressure, MAP, MAP in 10% decrements from baseline, and average cerebral oximetry index with MAP at the LLA. RESULTS： The MAP at the LLA was 66 mm Hg （95% prediction interval, 43 to 90 mm Hg） for the 225 patients in which this limit was observed.There was no relationship between preoperative MAP and the LLA （P = 0. 829） after adjusting for age, gender, prior stroke, diabetes, and hypertension, but a cerebral oximetry index value of 〉0.5 was associated with the LLA （P = 0. 022）. The LLA could be identified with cerebral oximetry index in 219 （94.4%） patients. The mean difference in the LLA for mean velocity index versus cerebral oximetry index was -0.2 〉 10.2 mm Hg （95% CI, - 1.5 to 1.2 mm Hg）. Preoperative systolic blood pressure was associated with a higher LLA （P = 0. 046） but only for those with systolic blood pressure ≤ 160 mm Hg. CONCLUSIONS： There is a wide range of MAP at the LLA in patients during CPB, making estimation of this target difficult. Real-time monitoring of autoregulation with cerebral oximetry index may provide a more rational means for individualizing MAP during CPB.