Optical monitoring and detection of spinal cord ischemia

Abstract

Spinal cord ischemia can lead to paralysis or paraparesis, but if detected early it may be amenable to treatment. Current methods use evoked potentials for detection of spinal cord ischemia, a decades old technology whose warning signs are indirect and significantly delayed from the onset of ischemia. Here we introduce and demonstrate a prototype fiber optic device that directly measures spinal cord blood flow and oxygenation. This technical advance in neurological monitoring promises a new standard of care for detection of spinal cord ischemia and the opportunity for early intervention. We demonstrate the probe in an adult Dorset sheep model. Both open and percutaneous approaches were evaluated during pharmacologic, physiological, and mechanical interventions designed to induce variations in spinal cord blood flow and oxygenation. The induced variations were rapidly and reproducibly detected, demonstrating direct measurement of spinal cord ischemia in real-time. In the future, this form of hemodynamic spinal cord diagnosis could significantly improve monitoring and management in a broad range of patients, including those undergoing thoracic and abdominal aortic revascularization, spine stabilization procedures for scoliosis and trauma, spinal cord tumor resection, and those requiring management of spinal cord injury in intensive care settings.

Figure 1. Fiber optic instrument validation.

(A) Detailed schematics of the experiment, featuring the instrument and its thin fiber optic probe. (B) In this experiment the instrument detected consistent physiologic changes due to three consecutive boluses of nitroprusside (gray arrows); the first bolus was 200 μg and the subsequent ones were 400 μg. Arrows indicate the time when the drug was administered. Each time point represents the mean value estimated by averaging the data from the two source-detector separations; the error bars represent the minimum and maximum blood flow/oxygenation changes measured across the source-detector separations. In the oxygen saturation time-course, the error bars also account for the uncertainty in the DPF assumed to estimate hemoglobin concentration changes. (MAP = mean arterial pressure, femoral (f) or carotid (c); ΔBF = changes in blood flow; ΔS_tO₂ = changes in tissue oxygen saturation).

Figure 2. Hemodynamic changes measured through different approaches.

Mean arterial pressure and hemodynamic changes measured during injection of boluses of phenylephrine injection (red arrow) followed by vasopressin injection (black arrow) in (A) subdural, (B) epidural, and (C) subdural positions after percutaneous approach. Arrows indicate the instant the drug was administered. Each time point represents the mean value estimated by averaging the data from the two source-detector separations; the error bars represent the minimum and maximum blood flow/oxygenation changes measured across the source-detector separations. In the oxygen saturation time-course, the error bars also account for the uncertainty in the DPF assumed to estimate hemoglobin concentration changes. (MAP = mean arterial pressure, femoral (f) or carotid (c); ΔBF = changes in blood flow; ΔS_tO₂ = changes in tissue oxygen saturation).

Figure 3. Hemodynamic monitoring during ischemia.

Blood flow (ΔBF), oxygen saturation (ΔS_tO₂) and mean arterial pressure (MAP, femoral (f) or carotid (c)) changes measured percutaneously during intra-aortic balloon inflation (grey area).