PROFOUND SYSTEMIC HYPOTHERMIA PROTECTS THE SPINAL-CORD IN A PRIMATE MODEL OF SPINAL-CORD ISCHEMIA

Spinal cord ischemia with resultant paraplegia or paraparesis remains an important clinical problem after operations on the thoracoabdominal aorta. Because hypothermia has a protective effect on ischemic neural tissue, we developed a baboon model of spinal cord ischemia to simula te the situation encountered clinically for resection of aneurysms of the thoracoabdominal aorta and to determine whether profound hypotherm ia produced by hypothermic cardiopulmonary bypass has a protective eff ect on spinal cord function. After cardiopulmonary bypass was establis hed, the aorta was clamped distal to the left subclavian artery and pr oximal to the renal arteries for 60 minutes. Group I animals (n = 9) u nderwent aortic clamping at normothermia (37-degrees-C), and group II animals (n = 9) were cooled to a rectal temperature of 15-degrees-C be fore aortic clamping and underwent cardiopulmonary bypass at this temp erature until the aorta was unclamped. Of the eight operative survivor s in group I, six animals were paraplegic and two were paraparetic, wh ereas all six group II animals that survived the procedure were neurol ogically intact (p = 0.0002). The protective effect of hypothermia was associated with blunting of the hyperemic response of spinal cord blo od flow (determined by the radioactive microsphere technique) in the l ower thoracic and the lumbar segments of the spinal cord after unclamp ing of the aorta. Profound hypothermia produced by hypothermic cardiop ulmonary bypass may be an effective method of protection of the spinal cord in patients undergoing repair of aneurysms of the thoracoabdomin al aorta and may reduce the prevalence of ischemic injury to the spina l cord.