Objective: Ischemic preconditioning has been found to protect various organs from a subsequent longer ischemic insult. We investigated whether the late phase of ischemic preconditioning reduces spinal cord injury from occlusion of the descending thoracic aorta.
Methods: Twenty-four pigs (27 to 30 kg) were randomly divided in four groups: group I (n = 4) underwent a sham operation, group II (n = 4) underwent aortic occlusion for 20 minutes, group III (n = 8) underwent aortic occlusion for 35 minutes, and group IV (n = 8) underwent aortic occlusion for 20 minutes and, 48 hours later, aortic occlusion for 35 minutes. Aortic occlusion was accomplished with two balloon occlusion catheters placed fluoroscopically at T(6) to T(8) above the diaphragm and at the aortic bifurcation. Neurologic evaluation was performed by an independent observer according to Tarlov's scale (0 to 4, with 4 as normal). The lower thoracic and lumbar spinal cords were harvested at 120 hours and examined histologically with hematoxylin and eosin stain. Histologic results (number of neurons and grade of inflammation) were scored 0 to 4 (4, intact spinal cord; 0, no neurons and high inflammation) and were similarly analyzed. Results were expressed as the mean +/- the standard error of the mean, and statistical analysis used the Kruskal-Wallis test.
Results: Group IV had a better neurologic outcome at 24, 48, and 120 hours in comparison with group III (P <.001), although 120 hours after the end of the experiment, the neurologic outcome in group IV was worse than at 24 hours (P =.014). The histologic changes were proportional to the neurologic test scores, with the more severe and extensive gray matter damage in the animals of group III (number of neurons, P <.001; and grade of inflammation, P <.001).
Conclusion: Ischemic preconditioning (late phase, 48 hours after the first occlusion) reduces spinal cord injury after aortic occlusion, as estimated with Tarlov's score and histopathology.