Developing a Real-Time, Axially Resolving Optical Monitor of Spinal Cord Blood Flow

BACKGROUND: Spinal cord ischemia is a disease of high morbidity and mortality often caused by surgeries repairing the thoracic and abdominal aorta. Current methods to monitor spinal cord hemodynamics such as electrophysiology methods, MR arterial spin labeling, and laser Doppler either have a slow response time or are unfeasible intra-operatively. In this study, we developed an optical probe to monitor spinal cord blood flow and oxygenation in real-time at multiple sites along the spine. METHODS: Experiments were conducted on 8 adult domestic pigs. Probes were inserted into the epidural space through a laminotomy prior to asphyxia and local ischemia via catheter balloon inflation. Vital signs, anesthetic parameters, and spinal hemodynamics were measured continuously prior to intervention, throughout asphyxia, and during inflation/deflation of the balloon catheter. Optical blood flow measurements were compared against microspheres. Optical hemoglobin saturation of spinal cord was compared to mixed venous blood gases. RESULTS: The fiber optic probe detected changes in flow and oxygenation in all asphyxia and balloon inflation trials across multiple sites along the spine. We observed significant changes in spinal cord blood flow during balloon inflation in the epidural space. We also observed a significant correlation between optically measured hemoglobin saturation and mixed venous blood gases. CONCLUSION: We developed an intra-operative tool that provides continuous, real-time monitoring of spinal cord hemodynamics at multiple sites along the spine. We hope this tool can more safely guide surgeons in reducing the incidence of spinal cord ischemia.