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 som atosensory 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. T his is the first study to compare the techniques directly during thoracoabd ominal aortic aneurysm repair. Methods in 38 patients, thoracoabdominal aortic aneurysm repair (type l, 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 indicat ors of cord ischemia. The authors compared the response of both methods to interventions and correlated the responses at the end ct surgery to neurolo gic outcomes. Results Ischemic tc-MEP changes occurred in 18/38 patients and could be res tored by segmental artery reperfusion (n = 12) or by increasing blood press ure (n = 6). Significant SSEP changes accompanied these tc-MEP events in on ly 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 amp litudes were 84 +/- 46% of control. In contrast, SSEP amplitudes were <50% of control in 15 patients (39%). No paraplegia occurred. Conclusion In ail patients, tc-MEP events could be corrected by applying pr otective strategies. No patient awoke paraplegic. SSEPs showed delayed isch emia detection and a high rate of false-positive results.