Accuracy and Applicability of Motor Evoked Potential Monitoring during Open Thoraco-Abdominal Aortic Aneurysm Repair

Spinal cord ischaemia (SCI) is a devastating risk in open thoraco-abdominal aortic aneurysm (TAAA) repair, making the reliable detection and prevention of neurological injury a clinical priority. The objective of this study was to evaluate the accuracy and clinical utility of motor evoked potential (MEP) monitoring in predicting and preventing SCI during open TAAA repair.

This retrospective case series study analysed 464 patients who underwent elective TAAA repair with MEP monitoring across two academic referral centres between 2000 and 2024. All procedures were performed by the same lead surgeon with an identical neurophysiological protocol. Clinically significant MEP changes were defined as a consistent decrease in leg to arm ratio by more than 50%. Post-operative neurological outcomes were categorised as acute, delayed, or uncertain SCI.

Clinically significant MEP changes occurred in 108 patients (23.3%), with recovery achieved in 99 cases (91.7%) following intra-operative measures to increase spinal cord perfusion. All nine patients without MEP recovery developed acute paraplegia. Among 356 patients with stable MEPs, none developed acute SCI, although 18 (5.1%) experienced delayed paraplegia associated with post-operative haemodynamic instability. The acute SCI rate was 1.9% (9 of 464), and any form of SCI (acute, delayed, or uncertain) occurred in 7.7% of cases (36 of 464). The absence of MEP signals at the end of the operation demonstrated 100% sensitivity, 100% specificity, and 100% negative and positive predictive values for acute SCI.

MEP monitoring is an excellent method, providing a proper execution and a compatible anaesthetic protocol, for detecting acute peri-operative SCI and greatly influences decision making to prevent acute SCI during open TAAA procedures, although delayed SCI remains an important factor that may not be detected by MEP changes alone, largely owing to factors occurring post-operatively.