Usefulness of transcranial motor evoked potentials during thoracoabdominal aortic surgery

Background. The purpose of this study was to evaluate the efficacy of myogenic transcranial motor evoked potentials (tc-MEPs) for spinal cord ischemia in the repair of descending thoracic or thoracoabdominal aortic aneurysms. Methods. Intraoperative tc-MEPs was used in 72 patients who underwent the repair of descending thoracic (n = 24) or thoracoabdominal aortic aneurysms ( n = 49) classed as Crawford 1 in 10 patients, II in 12, III in 23, and IV in 3. There were 52 men and 20 women, and their mean age was 64.9 +/- 12.8 years. Tc-MEPs were recorded by transcranial electrical stimulation and compound muscle action potentials. Results. The hospital mortality rate was 5.6% ( n = 4), and the incidence of neurologic deficits was 11.1% ( n = 8). All patients whose MEP amplitude recovered to more than 75% of the baseline showed normal spinal function, and 8 of 9 patients whose MEP amplitude decreased to below 75% of the baseline at the end of the procedure showed neurologic deficits postoperatively. The sensitivity of tc-MEPs was 100% and specificity was 98.4%. Latency in patients with postoperative paraplegia was 123% +/- 9% and was significantly prolonged at the end of the procedure. Conclusions. Tc-MEPs were very sensitive and specific to spinal cord ischemia with reduced amplitude and prolongation of the latency period. Tc-MEPs are considered a useful monitor of spinal cord ischemia during descending thoracic or thoracoabdominal aortic surgery. (c) 2007 by The Society of Thoracic Surgeons.