Non-invasive spinal cord oxygenation monitoring: validating collateral network near-infrared spectroscopy for thoracoabdominal aortic aneurysm repair.

Abstract

Near-infrared spectroscopy of the collateral network (cnNIRS) has recently been trialled to monitor real-time tissue oxygenation of the paraspinous vasculature as a surrogate for spinal cord tissue oxygenation. This large animal study was designed to investigate the correlation between cnNIRS and spinal cord oxygenation by comparing it to laser Doppler flowmetry (LDF), a proven method for direct oxygenation and flow assessment. Measurements were performed in seven animals. Four paravertebral cnNIRS optodes were positioned bilaterally at thoracic and lumbar levels to assess tissue oxygenation of the paraspinous vasculature. Paravertebral muscle and spinal cord oxygenation and microcirculatory flow were measured directly using LDF probes. LDF and cnNIRS were compared during consecutive repeated periods of descending aortic cross-clamping for 8 min and recovery by clamp release. Following aortic cross-clamping, lumbar cnNIRS signals instantaneously responded with a decrease to 85 ± 4% within 30 s, and to a minimum of 69 ± 6% after 8 min, returning to baseline values after clamp release within 40 s. Direct lumbar muscle and spinal cord oxygenation assessed by LDF responded analogously to cnNIRS (muscle and spinal cord oxygenation after cross-clamping 11.3 ± 6 and 37.6 ± 22% after 5 and 8 min, respectively). Comparison between lumbar cnNIRS and LDF muscle and spinal cord measurements showed a significant positive correlation (r = 0.51-0.52, P < 0.001). Thoracic cnNIRS signals remained relatively stable throughout the procedure. Lumbar paraspinous muscle oxygenation corresponded to direct spinal cord oxygenation (no significant difference, P = 0.296). These experiments confirm that the paraspinous vasculature in the presented large animal model is directly linked to spinal cord microcirculation and that the regional paraspinous muscle oxygenation status reflects spinal cord tissue oxygenation. As lumbar cnNIRS reproducibly depicts tissue oxygenation of the paraspinous vasculature, it can be used for non-invasive spinal cord oxygenation monitoring in real-time.