Transcutaneous near-infrared spectroscopy for monitoring spinal cord ischemia: an experimental study in swine

We aimed to assess the ability of near-infrared spectroscopy (NIRS) to detect spinal cord ischemia, and to evaluate changes in regional oxygen saturation (rSO₂) following recovery of spinal cord circulation and cerebrospinal fluid drainage. Four 12-month-old female swine weighing 28.7-29.5 kg were acquired for this study. NIRS probes were placed along the midline of the upper (T6/7) and lower (T9/T10) thoracic vertebrae. The thoracic aorta was clamped distal of the left subclavian artery to induce spinal ischemia. Aortic cross-clamping was maintained for 30 min. Fifteen minutes after aortic de-clamping, the cerebrospinal fluid drainage catheter was opened to air, and cerebrospinal fluid drainage was initiated. Following aortic clamping, rSO₂ in both upper and lower regions of the spinal cord decreased by 15 % within 5 min and by 20 % within 10 min (relative change). After aortic de-clamping, rSO₂ values in both regions returned to baseline within 5 min. No changes in rSO₂ in either the upper or lower vertebrae were observed following initiation of cerebrospinal fluid drainage. Histological analysis revealed that ischemic changes had occurred in all spinal levels. NIRS may be used to detect decreases in and recovery of spinal cord circulation following aortic clamping and de-clamping, whereas it may not reflect minor changes in spinal cord circulation due to cerebrospinal fluid drainage. Further clinical studies are required to investigate the potential for NIRS as an index of spinal cord circulation.