Fiber-optic Monitoring of Spinal Cord Hemodynamics in Experimental Aortic Occlusion

Abstract

BACKGROUND Spinal cord ischemia occurs frequently during thoracic aneurysm repair. Current methods to detect ischemia, based upon electrophysiology techniques, are indirect, non-specific, and temporally slow. Here we report the testing of a spinal cord blood flow and oxygenation monitor, based on Diffuse Correlation and Optical Spectroscopies, during aortic occlusion in a sheep model. METHODS Testing was carried out in sixteen Dorset sheep. Sensitivity in detecting spinal cord blood flow and oxygenation changes during aortic occlusion, pharmacologically induced hypotension and hypertension, and physiologically induced hypoxia/hypercarbia were assessed. Accuracy of the Diffuse Correlation Spectroscopy measurements was determined via comparison to microsphere blood flow measurements. Precision was assessed through repeated measurements in response to pharmacologic interventions. RESULTS The fiber optic probe can be placed percutaneously, and is capable of continuously measuring spinal cord blood flow and oxygenation preoperatively, intraoperatively, and postoperatively. The device is sensitive to spinal cord blood flow and oxygenation changes associated with aortic occlusion, immediately detecting a fall in blood flow (−65 ± 32%, n=32) and blood oxygenation (−17 ± 13%, n=11) in 100% of trials. Comparison of spinal cord blood flow measurements by the device with microsphere measurements led to a correlation of R2=0.49, p<0.01 and the within-sheep coefficient of variation was 9.69%. Finally, Diffuse Correlation Spectroscopy is temporally more sensitive to ischemic interventions than motor evoked potentials. CONCLUSIONS The first generation spinal fiber optic monitoring device offers a novel and potentially important step forward in the monitoring of spinal cord ischemia.

Spinal cord autoregulation using near-infrared spectroscopy under normal, hypovolemic, and post-fluid resuscitation conditions in a swine model: a comparison with cerebral autoregulation

“…NIRS estimates mixed tissue hemoglobin oxygen saturation levels of the arterial, venous, and capillary blood within the field of view [10,11], which allows the oxygen supply-and-demand balance to be evaluated under differing conditions. Similar to what has been done with the cerebrum, several studies have measured spinal cord oxygenation using NIRS directly [12][13][14][15] (via surgical procedure or thin fiber-optic probe placed in the intrathecal or epidural space) or indirectly [16][17][18][19] (via paraspinal muscle oxygenation monitoring, based on the paraspinal collateral network concept) to monitor spinal cord perfusion, but few studies to date have assessed spinal cord autoregulation using this method.…”

Spatially resolved optical monitoring of spinal cord blood flow with a minimally invasive, multi-level epidural probe

“…23 Our device has previously shown itself to rapidly (<10s) and reliably detect the onset of changes in blood flow. 31 Moreover, evoked potential monitoring cannot localize ischemia, complicating any attempt to restore blood flow via intraoperative re-implantation, etc. In the present work, our device has demonstrated its ability to spatially localize the level of aortic occlusion, potentially offering an improved opportunity for focused intervention.…”

Laser safety in fiber-optic monitoring of spinal cord hemodynamics: a preclinical evaluation

“…Recently, we developed and demonstrated continuous monitoring for spinal cord ischemia using a thin, flexible fiber-optic probe employing near-infrared (NIR) technology. 5,6 Furthermore, testing is needed prior to clinical adoption of this concept, including a clear demonstration that deployment of the required laser light in the proximity of the spinal cord is safe. This type of safety study is especially important because unlike many tissues in the body, even minimal damage to spinal tissues, as might arise in a "burn," can lead to paralysis or paraparesis.…”

“…Recently, we demonstrated and validated direct monitoring of spinal cord hemodynamics in sheep using a custom fiberoptic probe and optical monitor based on diffuse optical spectroscopy and diffuse correlation spectroscopy (DOS and DCS, respectively). 5,6 DCS is a relatively new technology capable of measuring microvascular blood flow. We have previously validated it against fluorescent microsphere measurements of spinal cord blood flow in a sheep model.…”

“…47 There have also been recent suggestions that light of similar wavelengths may be utilized to enhance healing of the spinal cord. 48,49 Our previous spinal cord work 5,6 focused on proof-of-concept demonstrations of optical monitoring of the spinal cord but did not address the safety of these measurements as pertains to optical spinal cord injury. Indeed, laser-related safety for long-term monitoring with diffuse light has never been tested in the spinal cord and these safety questions should be considered before moving these monitoring technologies to the spinal cords of human subjects.…”