SOMATOSENSORY-EVOKED POTENTIALS DURING EXCLUSION AND REPERFUSION OF CRITICAL AORTIC SEGMENTS IN THORACOABDOMINAL AORTIC-ANEURYSM SURGERY

Forty-three patients undergoing repair of a thoracoabdominal aortic an eurysm were monitored to evaluate spinal cord ischemia, as evidenced b y somatosensory evoked potentials (SEPs). All patients were operated o n using left heart bypass. In 34 patients (80%), staged clamping was u sed. Except for cerebrospinal fluid (CSF) drainage in 15 patients (35% ), no other protective measures to preserve spinal cord function were used. The overall incidence of immediate onset paraplegia was 7%, and of immediate onset paraparesis was 5%; neither was limited only to tho se patients in whom potentials were lost. In 18 patients (42%), no cha nge in the evoked potentials occurred; one of these patients (5%) awok e paraplegic after operation, and two others had a delayed onset parap legia. In 13 patients (30%), evoked potentials were lost despite adequ ate perfusion; in 12 of them, potentials returned gradually, with one immediate paraplegia (8%), and in one potentials did not return at all , with subsequent immediate paraplegia (100%). In 12 patients (28%), e voked potentials decreased without being lost completely, and then rec overed; in this group there were no immediate paraplegias. No relation ship could be demonstrated between the extinction time, the recovery t ime, or the duration of loss of evoked potentials with postoperative n eurological outcome. Intraoperative monitoring of SEPs is a good indic ator of spinal cord ischemia, although we found a 5% incidence of fals e negatives. SEP monitoring offers an improvement in surgical strategy , and allows safer operations for thoracoabdominal aneurysms.