PROTECTING THE ISCHEMIC SPINAL-CORD DURING AORTIC CLAMPING - THE INFLUENCE OF SELECTIVE HYPOTHERMIA AND SPINAL-CORD PERFUSION-PRESSURE

Purpose: We verified the hypothesis that selective deep hypothermia of the spinal cord during double thoracic aortic clamping can prevent po stoperative paraplegia in dogs. Methods: Normal saline solution was ci rculated from the cisterna magna through an extracorporeal perfusion s ystem consisting of a reservoir, a pump, and a heat exchanger, back in to the subarachnoid space at the level of the medullary cone at a rate of 25 ml/min, starting 30 minutes before clamping, and ending after r emoval of the clamps. The thoracic aorta was cross-clamped below the l eft subclavian artery and above the diaphragm for a period of 45 minut es. Cerebrospinal fluid, intracranial, and central venous pressure and aortic pressure proximal, between, and distal to the clamps were cont inuously recorded. In five dogs, temperature of the circulating normal saline solution at the inflow level was maintained at 2 degrees +/- 1 .5 degrees C (group 1), in five controls at 37 degrees +/- 0.8 degrees C (group 2). Five dogs underwent continuous cerebrospinal fluid drain age starting before clamping until sacrifice (group 3). Dogs were obse rved for up to 4 days, and neurologic function was graded by an indepe ndent observer with the Tarlov scale. Animals were then killed, and th eir spinal cords were prepared for microscopic examination. Results: H emodynamic parameters were not significantly different between groups. All dogs in groups 2 and 3 were paraplegic with histologic evidence o f spinal cord infarction. All animals in group 1 were neurologically n ormal without microscopic evidence of infarction (p < 0.005). Conclusi ons: Selective deep hypothermia of the spinal cord prevents paraplegia after 45 minutes of double aortic clamping in dogs. Cerebrospinal flu id drainage was not effective in preventing paraplegia in this model.