Continuous Cerebral Autoregulation Monitoring to Reduce Brain Injury from Cardiac

描述(申请人提供)：心脏手术期间的脑损伤主要是由于脑血栓和/或脑血流量(CBF)减少所致。后者尤其令人担忧的是越来越多的老年外科患者和/或患有脑血管疾病的患者。正常情况下，CBF在一定的血压范围内生理上自动调节(或保持恒定)，从而提供与代谢需求相适应的稳定的脑氧供应。在接受心脏手术的脑血管疾病患者和许多其他原因的患者中，大脑自动调节功能受损。这可能会导致脑损伤，因为目前在体外循环期间以低平均动脉压(通常为50-70毫米汞柱)为目标的做法可能会使脑自我调节受损的患者暴露于脑低灌流。这项建议的假设是，将体外循环期间的平均动脉压控制在高于个人较低自我调节阈值的水平，可以降低心脏手术患者脑损伤的风险。利用经颅多普勒测量的动脉血压与大脑中动脉血流速度的关系与近红外光谱分析的脑血氧饱和度的关系软件，实时进行脑自动调节的监测。这项研究的主要终点将是临床中风、认知能力下降和/或扩散加权磁共振(MR)成像检测到的新的缺血性脑损伤的综合结果。自我调节是由大脑阻力血管的反应性介导的。这项建议的第二个目的是评估近红外反射光谱是否可以用来跟踪脑血容量的变化，并提供可靠的血管反应性监测(血红蛋白体积指数)。将使用磁共振血管造影术对颅外和颅内动脉狭窄进行评估，以在分析中控制这一潜在的混杂变量。最后，这项研究的另一个目的是评估术前经颅多普勒检查主要大脑动脉是否可以确定哪些患者容易出现复合神经终点。近红外血氧仪是一种非侵入性的、连续的、几乎不需要护理者干预的方法，因此可广泛应用于术中患者的个体化血压管理。心脏手术引起的脑损伤是手术死亡率、住院时间延长、医疗费用增加和生活质量下降的重要原因。制定减轻这种并发症负担的战略具有广泛的公共卫生影响，也是NHLBI的任务之一。公共卫生相关性：心脏手术的神经系统并发症是手术死亡率、住院时间延长、医疗保健费用和生活质量受损的重要来源。需要新的护理策略，以避免越来越多的老年患者接受心脏手术时出现越来越多的并发症。这项研究将使用可以广泛应用的技术来评估减少手术中因脑血流不足而造成的脑损伤的新方法。

DESCRIPTION (provided by applicant): Brain injury during cardiac surgery results primarily from cerebral embolism and/or reduced cerebral blood flow (CBF). The latter is of particular concern for the growing number of surgical patients who are aged and/or who have cerebral vascular disease. Normally, CBF is physiologically autoregulated (or kept constant) within a range of blood pressures allowing for stable cerebral O2 supply commensurate with metabolic demands. Cerebral autoregulation is impaired in patients undergoing cardiac surgery who have cerebral vascular disease and in many others due to other conditions. This could lead to brain injury since current practices of targeting low mean arterial blood pressure empirically (usually 50-70 mmHg) during cardiopulmonary bypass may expose patients with impaired cerebral autoregulation to cerebral hypoperfusion. The hypothesis of this proposal is that targeting mean arterial pressure during cardiopulmonary bypass to a level above an individual's lower autoregulatory threshold reduces the risk for brain injury in patients undergoing cardiac surgery. Monitoring of cerebral autoregulation will be performed in real time using software that continuously compares the relation between arterial blood pressure and CBF velocity of the middle cerebral artery measured with transcranial Doppler and with cerebral oximetry measured with near infrared spectroscopy. The primary end-point of the study will be a comprehensive composite outcome of clinical stroke, cognitive decline, and/or new ischemic brain lesions detected with diffusion weighted magnetic resonance (MR) imaging. Autoregulation is mediated by reactivity of cerebral resistance vessels. A secondary aim of this proposal is to evaluate whether near infrared reflectance spectroscopy can be used to trend changes in cerebral blood volume and provide a reliable monitor of vascular reactivity (the hemoglobin volume index). Assessments for extra-cranial and intra-cranial arterial stenosis will be performed using MR angiography to control for this potential confounding variable in the analysis. Finally, an additional aim of the study will be to assess whether preoperative transcranial Doppler examination of major cerebral arteries can identify patients who are prone to the composite neurological end-point. Near infrared oximetry is non-invasive, continuous, requires little care- giver intervention and, thus, could be widely used to individualize patient blood pressure management during surgery. Brain injury from cardiac surgery is an important source of operative mortality, prolonged hospitalization, increased health care expenditure, and impaired quality of life. Developing strategies to reduce the burden of this complication has wide public health implications and is within the mission of the NHLBI. PUBLIC HEALTH RELEVANCE: Neurological complications from cardiac surgery are an important source of operative mortality, prolonged hospitalization, health care expenditure, and impaired quality of life. New strategies of care are needed to avoid rising complications for the growing number of aged patients undergoing cardiac surgery. This study will evaluate novel methods for reducing brain injury during surgery from inadequate brain blood flow using techniques that could be widely employed.