Pathogenesis of spinal cord injury during simulated aneurysm repair in a chronic animal model

Abstract

The pathogenesis of paraplegia after repair of thoracic aortic aneurysms is controversial. Using direct spinal cord evoked potential monitoring, critical intercostal arteries (CICA) were identified to evaluate the impact of backbleeding and ligation versus that of preservation during simulated aneurysm repair. Thirty pigs (40 kg) were randomly assigned to one of five groups. In groups 1 through 4, a thoracic segment containing CICA was cross-clamped for 60 minutes and distal aortic perfusion was provided by a centrifugal pump. In groups 1 and 2, the thoracic segment was vented, maintaining segment pressure at 0 mm Hg; CICA were ligated in group 1 and preserved in group 2. Thoracic segment was perfused at 70 mm Hg in groups 3 and 4; CICA were ligated in group 3 and preserved in group 4. Critical intercostal artery ligations were performed at the end of the cross-clamp period. In group 5 simple cross-clamping at the left subclavian artery was performed as a control. The combination of venting and ligation of CICA correlated with impaired neurologic outcome according to Tarlov's score (median, 1.5 in group 1 versus 3 in group 2; p = 0.015), indicated by a significant difference in median values of direct spinal cord evoked potential amplitude (expressed as a fraction of baseline values) at 120 minutes after cross-clamping (0.76 in group 1 versus 0.98 in group 2; p = 0.0082). Ligation of CICA without prior venting did not result in a significantly reduced Tarlov score (median, 3.5 in group 3 versus 4 in group 4; p = 0.182) and the difference in direct spinal cord evoked potential amplitude was less pronounced (0.85 in group 3 versus 1.0 in group 4, p = 0.0051). Simple cross-clamping caused paraplegia in all animals (group 5 versus group 1, p = 0.002). These results have prompted modifications of our operative strategy to include reattachment of CICA identified by monitoring of somatosensory evoked potentials and prevention of a steal phenomenon by serial intercostal ligation before aneurysm resection.