Experimental and clinical use of somatosensory evoked potentials in surgery of aneurysms of the descending thoracic aorta

The use of somatosensory evoked potentials (SEP) for the detection of spinal cord ischemia in surgery of the descending thoracic aorta was studied in nine dogs. Also 18 patients (group A) operated upon without distal aortic perfusion and 10 patients (group B) operated upon with distal aortic perfusion were studied. Tibial nerve stimulated SEP was used. Crude SEP characteristics and the reliability of SEP were assessed. In dogs the preservation of SEP corresponded with absence of neurological damage (p less than 0.02). Loss of SEP and late or absent recovery were associated with presence of neurological damage histopathologically proved (p less than 0.05). In group A SEP recording was affected by peripheral ischemia whereas this phenomenon was absent in group B during perfusion. In group A no relation was observed between the preservation, loss, and recovery of signal and the presence of neurological damage. In group B loss and recovery of SEP corresponded with assumed reperfusion of the spinal cord. Additional SEP recording obtained from stimulation of the skin overlying the fourth lumbar vertebra and of the medullary conus were preserved over a longer period. In patients this type of SEP was especially useful and reliable in case distal aortic perfusion was not used.