Is paraplegia after repair of coarctation of the aorta due principally to distal hypotension during aortic cross-clamping?

The hypothesis is presented that paraplegia after coarctation of the aorta is principally due to hypotension of sufficient severity and duration. In a group of 103 patients who underwent surgery during a 10-year period, the distal aortic pressure was maintained above 60 mm Hg while the aorta was cross-clamped or the period of cross-clamping was limited to less than 20 minutes. No neurologic problems occurred. In 17 of the 103 cases aortic pressure decreased below 60 mm Hg, occurring in 8% of patients with the aorta occluded below the left subclavian artery but in 30% of those occluded above. Therapeutic measures used in the 17 patients included infusion of metaraminol in five and limiting cross-clamp time to less than 20 minutes in 11. The theory is proposed that ligation of intercostal arteries in a patient with coarctation cannot injure the spinal cord because the normal direction of blood flow is reversed. Certainly, in patients without a coarctation, such as thoracic aneurysms, ligation of a critical intercostal artery may injure the spinal cord. However, in patients with coarctation the direction of blood flow is reversed, blood flowing from the intercostals into the distal aorta. The vague relationship long noted between development of collateral circulation, including rib notching, and the frequency of paraplegia probably depends not on the presence of enlarged intercostal arteries but on whether their temporary occlusion at the time of aortic cross-clamping results in distal hypotension. Data with somatosensory-evoked potentials measured during operations on the thoracic aorta in 25 patients found no changes in sensory potentials as long as the distal aortic pressure remained above 60 mm Hg, but a gradual disappearance was found at lower pressures. In five of six patients with large thoracicoabdominal aneurysms in whom sensory potentials were absent for longer than 30 minutes, paraplegia resulted. Use of somatosensory potentials provides a significant method for evaluating methods to protect from paraplegia. This method should be far more productive than are simple clinical experiences because the fortunate rare occurrence of paraplegia, one in 200, greatly limits available data.