Comparison of transcranial motor evoked potentials and somatosensory evoked potentials during thoracoabdominal aortic aneurysm repair.

OBJECTIVE To compare transcranial motor evoked potentials (tc-MEPs) and somatosensory evoked potentials (SSEPs) as indicators of spinal cord function during thoracoabdominal aortic aneurysm repair. SUMMARY BACKGROUND DATA Somatosensory evoked potentials reflect conduction in dorsal columns. tc-MEPs represent anterior horn motor neuron function. This is the first study to compare the techniques directly during thoracoabdominal aortic aneurysm repair. METHODS In 38 patients, thoracoabdominal aortic aneurysm repair (type I, n = 10, type II, n = 14, type III, n = 6, type IV, n = 8) was performed using left heart bypass and segmental artery reimplantation. tc-MEP amplitudes <25% and SSEP amplitudes <50% and/or latencies >110% were considered indicators of cord ischemia. The authors compared the response of both methods to interventions and correlated the responses at the end of surgery to neurologic outcomes. RESULTS Ischemic tc-MEP changes occurred in 18/38 patients and could be restored by segmental artery reperfusion (n = 12) or by increasing blood pressure (n = 6). Significant SSEP changes accompanied these tc-MEP events in only 5/18 patients, with a delay of 2 to 34 minutes. SSEPs recovered in only two patients. In another 11 patients, SSEP amplitudes fell progressively to <50% of control without parallel tc-MEP changes or association with cross-clamp events or pressure decreases. At the end of the procedure, tc-MEP amplitudes were 84 +/- 46% of control. In contrast, SSEP amplitudes were <50% of control in 15 patients (39%). No paraplegia occurred. CONCLUSION In all patients, tc-MEP events could be corrected by applying protective strategies. No patient awoke paraplegic. SSEPs showed delayed ischemia detection and a high rate of false-positive results.