PATHOGENESIS OF SPINAL-CORD INJURY DURING SIMULATED ANEURYSM REPAIR IN A CHRONIC ANIMAL-MODEL

The pathogenesis of paraplegia after repair of thoracic aortic aneurys ms is controversial. Using direct spinal cord evoked potential monitor ing, critical intercostal arteries (CICA) were identified to evaluate the impact of backbleeding and ligation versus that of preservation du ring simulated aneurysm repair. Thirty pigs (40 kg) were randomly assi gned to one of five groups. In groups 1 through 4, a thoracic segment containing CICA was cross-clamped for 60 minutes and distal aortic per fusion was provided by a centrifugal pump. In groups 1 and 2, the thor acic segment was vented, maintaining segment pressure at 0 mm Hg; CICA were ligated in group 1 and preserved in group 2. Thoracic segment wa s 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 cros s-clamping at the left subclavian artery was performed as a control. T he combination of venting and ligation of CICA correlated with impaire d 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 differe nce in median values of direct spinal cord evoked potential amplitude (expressed as a fraction of baseline values) at 120 minutes after cros s-clamping (0.76 in group I versus 0.98 in group 2; p = 0.0082). Ligat ion of CICA without prior venting did not result in a significantly re duced 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 amplitu de was less pronounced (0.85 in group 3 versus 1.0 in group 4, p = 0.0 051). Simple cross-clamping caused paraplegia in all animals (group 5 versus group I, 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 stea l phenomenon by serial intercostal ligation before aneurysm resection.