Study of Regional Cerebral Oxygenation and Brain Blood Volume Changes During Cardiac Surgery Using the NeurOS System

1. Title of the Research Project： Study of regional Cerebral Oxygenation and Brain Blood Volume changes during Cardiac Surgery using the NeurOS system (COBBV-CS 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."

The data is controversial on the benefits of NIRS to prevent or reduce stroke or delirium after cardiac surgery. However, it must be realized the inherent limitations of monitors alone to impact clinical outcomes without a standardized intervention algorithm. Although multiple NIRS monitors are approved in the United States and other countries primarily for assessing the adequacy of cerebral oxygenation during surgery, their approval is not based on the indication of detecting and/or lowering the frequency of neurological complications. In regard to the latter, strokes are believed widely to result primarily from cerebral embolism and/or cerebral hypoperfusion. Importantly, both etiologies can contribute to cerebral injury in the same patient insofar as hypoperfusion may delay washout of microembolism and/or compromise collateral perfusion to the ischemic penumbra. Many strokes, though, occur in subcortical brain areas or at sites remote from the area of NIRS monitoring, and many occur in the postoperative period after NIRS monitoring has concluded.

In addition, technological advances with NIRS monitoring have continued and now include the ability to perform bedside cerebral autoregulation monitoring. 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 during CPB, 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.

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. The investigators will use NeurOS in accordance with its approved labeling and indications by FDA. Cardiac surgery has significant variations and great clinical importance of cerebral oxygenation during different stages of surgery. Blood volume changes before, during and after cardiopulmonary bypass 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.

3. Objectives: