Epidural cooling minimizes spinal cord injury after aortic cross-clamping through induction of nitric oxide synthase

BACKGROUND: By using a U-shaped lumen catheter, the authors examined the effects of epidural cooling on spinal cord injury after aortic cross-clamping (ACC), with a focus on changes of spinal cord blood flow and expression of inducible nitric oxide synthase. METHODS: Sixteen pigs were randomized into two groups: Control group (n = 8) or Cooling group (n = 8). In the latter, epidural cooling started at 30 min (baseline) before 45 min of ACC and persisted for the next 30 min of reperfusion period. Spinal cord blood flow and somatosensory-evoked potentials were assessed during peri-ACC period. At 48 h, we evaluated hind limb function by using Tarlov score and expression of inducible nitric oxide synthase on spinal cord using immunohistochemistry. RESULTS: After ACC, spinal cord blood flow dropped to a similar extent in both groups. During the reperfusion period, spinal cord blood flow increased up to 113% (103-124%), median (interquartile range), level transiently and decreased to 32% (22-47%) level versus baseline in the Control group, whereas it increased and remained at 92% (86-97%) level in the Cooling group. Simultaneously, somatosensory-evoked potentials showed that onset of loss time was delayed and recovery time was shortened in the Cooling group. Tarlov scores in the Cooling group were significantly higher and accompanied by normal-appearing motor neurons and significantly greater expression of inducible nitric oxide synthase on spinal cord versus the Control group. CONCLUSIONS: This study shows that epidural cooling during ACC minimized the risk of spinal cord injury, possibly by preventing delayed hypoperfusion and upregulating inducible nitric oxide synthase expression.