The mechanism of spinal cord injury after simple and double aortic cross-clamping.

Ischemic spinal cord injury after cross-clamping of the descending aorta can occur independently of aortic disease. In a previous study we had shown a precipitous uniform fall of spinal surface oxygen tension downstream to the clamping site irrespective of level. In the present paper, the hemodynamic changes in the spinal and aortic collateral circulation were investigated. Pressures were measured in the proximal, distal, and excluded aortic segments (descending thoracic and lumbar aorta) as well as in the intercostal and the lumbar arterial beds. Before high aortic occlusion, pressures in the intercostal and lumbar arterial beds were lower than aortic pressure. Along with the postclamping fall in distal arterial pressure, intercostal and lumbar arterial bed pressure decreased further but remained above aortic pressure. Exclusion of the thoracic aorta by double clamping restored intercostal bed pressure almost to control, whereas exclusion of the abdominal aorta hardly affected lumbar bed pressure. We conclude that spinal collateral circulation is more highly developed in the thoracic than in the lumbar region. After aortic cross-clamping, blood tends to drain away from the spinal cord rather than supplying it longitudinally. Under clinical conditions, therefore, retrograde bleeding into the opened aorta as well as into the aorta downstream to the distal clamp should be minimized and larger vessels originating from the aorta should promptly be anastomosed to the graft.