Repair of the descending thoracic aorta: impact of open distal anastomosis technique on spinal cord perfusion, neurological outcome and spinal cord histopathology.

OBJECTIVES: We investigated the impact of equilibrating distal aortic pressure with atmospheric pressure (open distal anastomosis) on spinal cord perfusion, neurological outcome and spinal cord histopathology in a rat model of descending thoracic aortic surgery.

METHODS: Proximal thoracic aortic occlusion was obtained in Sprague-Dawley rats by inflating the balloon of a 2F Fogarty catheter introduced through the left femoral artery. Rats were separated into three groups: sham-operation (n = 5) without balloon inflation, control (n = 15) with inflation of the balloon, and open distal (n = 15) with inflation of the balloon combined with incision of the right femoral artery to allow free drainage of distal aortic blood. Balloon inflation was maintained for 15 min. Rectal temperature, arterial blood gases and pH, distal arterial blood pressure (DABP) and lumbar spinal cord blood flow (SCBFl) were recorded throughout the procedure. Neurobehavioral status was assessed daily using a 0-5 scale and rats were sacrificed after 48 h of reperfusion and their spinal cord harvested for histopathology and immunohistochemistry for microtubule-associated protein-2 (MAP-2).

RESULTS: DABP and SCBFl values were lower during thoracic aortic occlusion in the open distal group, compared to the control group (P < 0.001). Paraplegia and mortality rates were dramatically increased in the open distal group (87.7 and 46.6%, respectively) compared to the control group (0 and 6.6%, respectively, (P < 0.001 and 0.02). Severe metabolic acidosis and bowel infarct were also more frequent in the open distal group (P < 0.001). Sham-operated and control rats had virtually normal spinal cords, whereas rats in the open distal group had severe ischemic injury throughout gray matter.

CONCLUSIONS: Equilibrating distal arterial pressure with atmospheric pressure during thoracic aortic occlusion decreased spinal cord blood flow, increased mortality and worsened spinal cord injury in rats. These results suggest that the open distal anastomosis technique should be used with caution in patients undergoing repair of the descending thoracic or thoracoabdominal aorta.