Detection of Cerebral Ischemia With a Noninvasive Neurometabolic Optical Monitor

Many critically ill patients are admitted to the hospital with no infarcted brain tissue and yet, after a period of extremely intense and expensive critical care, the patients are discharged with new hospital-acquired dead brain tissue, with associated life-long disability or brain death. This situation arises from the critical barrier of there being no straightforward bedside methods to monitor cerebral blood flow (CBF) and its adequacy during progression of post-insult secondary brain damage. This is important because of the expectation that decrements in CBF in dangerous excess of decrements in cerebral metabolic rate for oxygen (CMRO2), if detected early, can be treated to avert brain infarction. Clinical examples of this issue, among many others, include post ischemic stroke edema, post thrombolysis hyperemia or occlusion, post SAH vasospasm, hyperemic and oligemic intracranial hypertension after traumatic brain injury or stroke, ICH associated global ischemia, and intra and post carotid endarterectomy oligemia and hyperperfusion. Critical care physicians need a bedside monitor of CBF coupled to CMRO2. The CMRO2 data will allow delineation of adequacy of CBF as occasionally CBF decrements are simply matching changes in CMRO2. The lack of such monitoring capability has resulted in clinicians making often not helpful therapeutic decisions directed to non-neurologic endpoints, e.g., blood pressure, PaCO2 and so on, "hoping" that such interventions will have a desired effect on brain perfusion and metabolism. Diffuse Correlation Spectroscopy (DCS) and Diffuse Optical Spectroscopy (DOS) are promising NNOM optical techniques under development at UPenn (Dr. Arjun Yodh) which can provide continuous bedside quantitative CBF, CMRO2 and oxygen extraction fraction (OEF) information. Determination of capability to detect anaerobic conditions, as the investigators propose doing, will make feasible the notion of individualized CBF, CMRO2, and OEF measurement and brain-directed therapeutic optimization by bedside caregivers. This will eventually support a significant change in the way Neurocritical Care is practiced, titrating therapy to neurophysiologic rather than cardiovascular/ pulmonary endpoints. UPenn research techniques presently provide information on relative quantitative changes in CBF and CMRO2 from baseline. The investigators propose also developing a method for measurement of absolute CBF and CMRO2 and further validating the absolute CBF against invasive thermodilution (ThD) CBF techniques. The investigators' long range goal and overall objective is to prevent in-hospital brain tissue death through development of improved bedside CBF/ CMRO2/OEF (NNOM) monitoring techniques.