Measurement of spinal cord ischemia during operations upon the thoracic aorta: initial clinical experience

Paraplegia has been an unpredictable, devasting complication following operations upon the thoracoabdominal aorta for over 30 years. The frequency ranges from 0.5% with operations for coarctation to as high as 15% following surgery for thoracoabdominal aneurysms. Both uncertainty and controversy exist about the value of different protective methods during aortic crossclamping (AXC): heparinized shunts, partial bypass, and reimplantation of intercostal arteries. This report describes the authors' initial clinical experience with a highly sensitive indicator of spinal cord ischemia, somatosensory evoked potentials (SEP) in an attempt to prevent paraplegia associated with surgical procedures on the thoracoabdominal aorta. Seven consecutive patients (one coarctation, five thoracic aneurysms, one thoracoabdominal aneurysm) underwent continuous operative monitoring of SEP. Cortical response to simultaneous electrical stimulation (20 mAmps, 0.6 mSec., 2.3 cps) of both the right and left posterior tibial nerves was recorded before, during, and after AXC, and following operation. When ischemic changes were detected by SEP, increasing distal circulation by different maneuvers (heparinized shunt, femoral-femoral bypass, reimplantation of intercostal arteries) reversed these changes. In two patients with thoracic aneurysms, ischemic changes appeared within three minutes after AXC and all potentials disappeared in nine minutes. Rapid insertion of a graft (AXC 28 and 37 minutes) resulted in SEP return 40 minutes following restoration of flow. These changes were prevented by a heparinized shunt in two patients, femoral/femoral bypass in one, and T8-T9 intercostal reimplantation in one. No SEP changes occurred in the patient with coarctation. No postoperative neurologic complications occurred. Continuous operative monitoring of SEP has exciting possibilities for preventing paraplegia. It is simple, highly sensitive, and seems to provide a precise measurement of adequacy of circulation to the spinal cord.