Noninvasive optical assessment of neuroprotection in deep hypothermic circulatory arrest procedures

Massachusetts General Hospital, Boston MA

Investigators

Abstract

PROJECT SUMMARY Neurologic dysfunction is a major concern for patients and clinicians as it significantly contributes to high morbidity and mortality, negatively affect patients’ quality of life and increase healthcare cost. Despite substantial technological advancements in surgery, cardiopulmonary bypass (CPB) and anesthesia, cardiac surgery carries substantially high incidence of neurologic dysfunction such as stroke, delirium and cognitive dysfunction. Aortic arch surgery involving partial or complete replacement of the aortic arch to treat aortic aneurysm and dissections is associated with the highest rates of neurologic dysfunction in cardiac surgery, assumed to be largely due to brain ischemia during the circulatory arrest (CA) period required for the surgery. To limit neurologic injury risks, several neuroprotective strategies are employed, including hypothermia and supplemental cerebral perfusion delivered either in antegrade (ACP) or retrograde (RCP) fashion. While certain areas of consensus are starting to emerge in the field (e.g. the degree of hypothermia, duration of CA, and unilateral or bilateral ACP), the picture remains complex. The primary goal of supplemental perfusion is to restore cerebral perfusion and oxygen delivery during prolonged period of CA required for majority of aortic arch surgery. The optimal flow from ACP is unknown and there are concerns of cerebral damage from blood overflow and emboli from ACP. The efficacy of RCP has also been questioned as there is no evidence showing the blood from RCP to circulate through the brain. Our team has piloted the use of diffuse correlation spectroscopy (DCS) for cerebral perfusion monitoring in a recent observational study. We demonstrated that DCS records extremely low brain tissue perfusion from RCP during CA in agreement to previous animal studies. In addition, we measured cerebral blood flow from ACP that was higher during CA than that of cerebral blood flow on cardiopulmonary bypass. We propose to expand on this work to conduct a comprehensive study of patients undergoing aortic arch surgery under hypothermic CA (HCA), with supplemental perfusion of either type, to better understand the correlation between different brain protection strategies, neurologic injury and mechanisms of neurocognitive deficit development, in both the short and medium term. Optical monitoring of cerebral perfusion and oxygenation will be combined with MRI assessments, blood biomarker assays and cognitive evaluation to characterize the effectiveness of HCA supplementary perfusion strategies, and to disentangle the contributions of perfusion deficits and ischemia from emboli generation and neurotoxic biochemical elevations (e.g. phosphorylated tau proteins, recently shown to correlate with the occurrence of delirium after major cardiac surgery).