Measuring CMAPs in addition to MEPs can distinguish peripheral ischemia from spinal cord ischemia during endovascular aortic repair

OBJECTIVE: Spinal cord injury is a devastating complication after endovascular thoracic and thoracoabdominal aneurysm repair (EVAR). Motor evoked potentials (MEPs) can be monitored to detect spinal cord injury, but may also be affected by peripheral ischemia caused by femoral artery sheaths. We aimed to determine the incidence of peripheral ischemia during EVAR, and whether central and peripheral ischemia can be distinguished using compound muscle action potentials (CMAPs). METHODS: We retrospectively analyzed all EVAR procedures between March 1st 2015 and January 1st 2020 during which MEPs were monitored. Peripheral ischemia was defined as both a reduction in MEP amplitudes reversed by removing the femoral sheaths and no clinical signs of immediate post-procedural paraparesis. All other MEP decreases were defined as central ischemia. RESULTS: A significant MEP decrease occurred in 14/27 (52%) of all procedures. Simultaneous CMAP amplitude reduction was observed in 7/8 (88%) of procedures where peripheral ischemia occurred, and never in procedures with central ischemia. CONCLUSIONS: MEP reductions due to peripheral ischemia are common during EVAR. A MEP-reduction without a CMAP decrease indicates central ischemia. SIGNIFICANCE: CMAP measurements can help to distinguish central from peripheral ischemia, potentially reducing the chance of misinterpreting of MEP amplitude declines as centrally mediated, without affecting sensitivity.