Somatosensory evoked potential monitoring of spinal cord ischemia during aortic operations.

Somatosensory evoked potentials were monitored in 22 consecutive patients undergoing surgical correction of an aortic coarctation. Induction of spinal cord ischemia by cross clamping of the aorta elicited a change in the evoked potential in 9 patients (41%). These alterations occurred within 5 minutes of aortic clamping in 3 cases and after 18 to 21 minutes in the remaining 6 cases. Loss of the somatosensory evoked potential for more than 14 minutes was associated with postoperative neurological deficit. Alteration of the evoked potential within 5 minutes of aortic cross clamping was significantly related to poor collateral circulation shown on the preoperative aortogram. The pathophysiology of evoked potential changes in spinal ischemia is discussed in detail.