Evaluation of spinal cord function by means of lower limb somatosensory evoked potentials in reparative aortic surgery.

ABSTRACT

A group of patients undergoing aortic replacement of thoracic and abdominal aneurysms were studied by intraoperative recording of Somatosensory Evoked Potentials (SEPs). Lower limb nerves were stimulated and SEPs recorded at spinal and cortical level. Progressive changes of cortical SEPs until their disappearance were observed. In operations on the thoracic aorta, the spinal response was essentially unmodified, so that the observed alterations reflected true dysfunction of the spinal cord. The only patient who developed an intraoperative anterior spinal infarct had the longest period of absent SEPs and a striking latency prolongation when they returned. Postoperative recordings were absolutely normal. When the abdominal aorta was occluded, SEP alterations involved both cortical and spinal responses, so that it is difficult to distinguish between the relative roles of peripheral nerve and spinal cord ischemia. These findings indicate that SEPs can be reliably applied to spinal cord monitoring in the course of aortic surgery, even though they are mainly conducted in the posterior cord tracts.