Study of Regional Cerebral Oxygenation and Brain Blood Volume Changes During Carotid Endarterectomy Using the NeurOS System

1. Title of the Research Project： Study of Regional cerebral Oxygenation and Brain Blood Volume change during Carotid Endarterectomy using the NeurOS system (COBBV-CE Trial)
2. Background/Problem Statement: The use of regional cerebral oxygenation (rSO2) monitoring has grown clinically, even becoming the standard of care in some institutions. Monitoring of intracranial tissue oxygenation is fundamentally possible because light in the near infrared spectrum (700-900nm) penetrates bone, muscle, and other tissue. Oxyhemoglobin and deoxyhemoglobin have distinct peak absorption spectra, but there is an isobestic wavelength (i.e., wavelength for which the peak absorption of light is similar for oxyhemoglobin and deoxyhemoglobin, approximately 810nm) for absorption by total hemoglobin. Determination of rScO2 thus is possible with transmission of just 2 wavelengths of near-infrared spectroscopy (NIRS) to determine the relative concentrations of oxyhemoglobin versus total hemoglobin. A decrease in rSO2 from baseline >20% or an absolute rSO2 value <50% often is reported in clinical investigation as representing a clinically meaningful reduction or "desaturation."

Cerebral autoregulation was found to be impaired in carotid stenosis patients. Recent research found that NIRS allows continuous non-invasive monitoring of cerebral oxygenation during CEA, with high sensitivity and acceptable specificity in predicting cerebral ischemia and the need for shunting, which makes it an attractive alternative to stump pressure. Regional cerebral oxygenation provides a clinically acceptable surrogate of cerebral blood flow (CBF) for clinical autoregulation monitoring. Monitoring CBF autoregulation with rSO2 has many clinically attractive features, including the following: It is noninvasive, monitoring requires little caregiver intervention, and it has sufficient resolution to discriminate the lower autoregulatory threshold to prevent brain ischemia. On the other hand, simply raising mean blood pressure targets, however, may not necessarily be beneficial because for some individuals this may result in blood pressure above the upper limit of autoregulation, which potentially could lead to cerebral hyperperfusion, increasing cerebral embolic load and/or enhancing cerebral edema in the setting of systemic inflammatory response to cardiac surgery. Individualizing blood pressure during CPB based on physiological endpoints such as rSO2 monitoring, rather than empiric targets, may provide a means for modifying the risk for renal injury and major organ morbidity and possibly mortality. In patients undergoing combined CEA and CABG surgery, it was found that the utility of NIRS could compliment patient selection for CEA as well as for individual patient management during. The brain blood volume changes during CEA has not been defined and would be significantly reduced by carotid artery clamping during CEA. Abnormalities of the circle of Willis would contribute to reduced brain blood volume. The combination of rSO2 and cerebral blood volume would be very helpful to prevent mal-perfusion of either side of the brain. Postoperative delirium could happen after CEA due to reperfusion of the previously ischemic regions of the brain, regulation of cerebral blood volume after CEA would also prove beneficial to prevent postoperative delirium.

Problem Statement: Disposable rSO2 sensors are costly and is becoming a rate limiting factor hindering its widespread clinical use. Reusable sensors like NeurOS cerebral oximetry are only a fraction of cost with similar performances in healthy volunteers. We will use NeurOS in accordance with its approved labeling and indications by FDA. CEA surgery has significant variations and great clinical importance of cerebral oxygenation during different stages of surgery. Blood volume changes before, during and after CEA have not been studied previously and could provide critical information to prevent postoperative cognitive changes. The NeurOS system calculates the sum of attenuation of two wavelengths to provide brain blood volume index (BVI) continuously.

Patients presenting for carotid endarterectomy face two challenges during surgery. First, how to protect the brain when the carotid artery is clamped, meaning no blood flow to that side of the brain from this carotid artery. Second, how to prevent hyperemia when the carotid artery is open and might provide too much blood flow to the brain. Our aim is to study the cerebral oxygenation and brain blood volume changes during carotid endarterectomy and identify whether they are related to clinical outcomes.

3. Objectives: