[The prevention of spinal cord ischemia during the operation on the thoracic aorta utilizing the evoked spinal cord potential (ESP)].

The evoked spinal cord potential was used for the moniter of the spinal cord ischemia during the operation on the thoracic aorta. At first, experiments were performed on 23 dogs. Following laminectomy and 1t. thoracotomy, evoked spinal cord potential to the stimulation from bipoler electrodes in the midline dorsal subdural space at the level of near L1 were recorded from needle electrode in the intervertebral disk at the level of Th4-5. After baseline measurements, the thoracic aorta was occluded in all dogs by aortic cross-clamping (AXC) distral to the origin of the left subclavian artery. Then 3 types of changes were detected. TYPE-I (n = 8) showed loss of the ESPs during AXC and return after reperfusion. TYPE-II (n = 10) showed no changes during and after AXC. TYPE-III (n = 5) showed return of ESPs after transient loss of them even during AXC. Five of 7 dogs (71%) in TYPE-I and 1 of 5 dogs (20%) in TYPE-III developed paraplegia, but all of them in TYPE-II avoided paraplegia. Secondly, ESP was used for the moniter of spinal cord ischemia during operation on 13 patients. Ten patients showed no changes of ESPs, but 3 showed loss of ESPs during AXC and return after reperfusion of them. No paraplegia appeared. We have concluded that intraoperative ESP monitering is a more reliable indicator of the spinal cord ischemia than other methods previously reported.