Somatosensory evoked potentials during reversible spinal cord ischemia in man.

Somatosensory evoked potentials (SEPs) from peroneal nerve were recorded continuously on 13 patients undergoing extensive aortic replacement of thoracic, abdominal, or thoracico-abdominal aneurysms. During this surgical procedure, the descending aorta is completely occluded, and circulation to the spinal cord may thus be compromised, causing a risk of postoperative paraplegia. This risk may be minimized if changes in the SEP seen during intraoperative monitoring prove to correlate well with clinical outcome. Changes in the SEP observed during complete occlusion of the aorta and subsequent restoration of blood flow included: (1) progressive latency prolongation within the first 10 min of occlusion, (2) coincident and progressive amplitude depression, (3) eventual loss of the SEP, (4) rapid reversal of these changes with restoration of circulation, and (5) preservation of the lumbar response when the cephalic response became abnormal. The degree of prolongation of latency after restoration of blood flow appeared related to the duration of aortic occlusion and to the duration of SEP absence. These findings indicate that conduction through the spinal pathways that mediate the SEP is sensitive to ischemia produced by aortic occlusion. Intraoperative monitoring of SEPs as a means of reducing the neurological morbidity of extensive aortic replacement is discussed.