Continuous Cerebral Autoregulation Monitoring to Reduce Brain Injury from Cardiac

描述（由申请人提供）：心脏手术中的脑损伤主要由脑栓塞和/或脑血流量减少（CBF）引起。对于越来越多的老年和/或患有脑血管疾病的外科病人来说，后者尤其值得关注。正常情况下，脑血流在生理上自动调节（或保持恒定）在血压范围内，允许稳定的脑氧供应与代谢需求相称。在患有脑血管疾病的心脏手术患者和许多其他因其他条件而受损的患者中，大脑自身调节功能受损。这可能导致脑损伤，因为目前在体外循环过程中以经验为目标的低平均动脉血压（通常为50-70 mmHg）的做法可能使脑自动调节受损的患者暴露于脑灌注不足。该建议的假设是，在体外循环过程中，将平均动脉压控制在高于个体较低的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。使用软件实时监测大脑自动调节，持续比较经颅多普勒测量的动脉血压和大脑中动脉血流速度与近红外光谱测量的脑血氧仪之间的关系。该研究的主要终点将是临床卒中、认知能力下降和/或扩散加权磁共振（MR）成像检测到的新缺血性脑病变的综合综合结果。自我调节是由脑阻力血管的反应性介导的。本提案的第二个目的是评估近红外反射光谱是否可以用于脑血容量的变化趋势，并提供血管反应性（血红蛋白体积指数）的可靠监测。颅外和颅内动脉狭窄的评估将使用MR血管造影进行，以控制分析中这一潜在的混杂变量。最后，本研究的另一个目的是评估术前经颅多普勒脑大动脉检查是否可以识别容易出现复合神经终点的患者。近红外血氧测量是非侵入性的，连续的，几乎不需要护理人员的干预，因此，可以广泛应用于手术期间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。制定战略以减轻这一并发症的负担具有广泛的公共卫生影响，并且属于卫生和健康机构的任务范围。公共卫生相关性：心脏手术引起的神经系统并发症是手术死亡率、住院时间延长、卫生保健支出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并发症。本研究将评估可广泛应用的新方法，以减少手术中因脑血流不足而造成的脑损伤。

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.