Commentary: Evoked potential monitoring during open distal repair predicts spinal cord ischemic injury-but does it prevent it?

Central MessageEvoked potential monitoring during open distal repair predicts spinal cord ischemic injury, but its role in preventing injury has not been clearly established.See Article page 944. Evoked potential monitoring during open distal repair predicts spinal cord ischemic injury, but its role in preventing injury has not been clearly established. See Article page 944. Spinal cord ischemic injury (SCII), manifested clinically by permanent paraplegia or paraparesis, is the most devastating complication following open repair of descending thoracic and thoracoabdominal aortic aneurysms. Interventions that have been implemented to limit the occurrence of permanent SCII include distal aortic perfusion, drainage of cerebral spinal fluid, implantation of intercostal and lumbar arteries, hypothermia, and the use of pharmacologic neuroprotective agents (glucocorticoids, barbiturates, opioid antagonists, and papaverine). Monitoring of sensory- (SSEP) and motor-evoked potentials (MEP) has also been used in some centers to detect SCII intraoperatively and to then initiate maneuvers to reverse the ischemic injury. At present, monitoring of evoked potentials according to North American and European consensus panels is a Class B1Hiratzka L.F. Bakris G.L. Beckman J.A. Bersin R.M. Carr V.F. Casey Jr., D.E. et al.2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with thoracic aortic disease: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines, American Association for Thoracic Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine.Circulation. 2010; 121: e266-e369Crossref PubMed Scopus (2038) Google Scholar or IIb2Etz C.D. Weigang E. Martert M. Lonn L. Mestres C.A. Di Bartolomeo R. et al.Contemporary spinal cord protection during thoracic and thoracoabdominal surgery and endovascular repair: a position paper of the vascular domain of the European Association for Cardio-Thoracic Surgery.Eur J Cardiothorac Surg. 2015; 47: 943-957Crossref PubMed Scopus (179) Google Scholar intervention and is limited to patients whose operative procedures are performed under normothermic or mild hypothermic conditions. In this issue of the Journal, Tanaka and colleagues3Tanaka A. Nguyen H. Dhillon J.S. Nakamura M. Zhou S.-F. Sanhu H.K. et al.Reappraisal of the role of motor and somatosensory evoked potentials during open distal aortic repair.J Thorac Cardiovasc Surg. 2023; 165: 944-953Abstract Full Text Full Text PDF Scopus (2) Google Scholar present their extensive experience with neuromonitoring of SSEP and MEP in 822 patients undergoing open repair of thoracic (n = 309) and thoracoabdominal (n = 513) aortic aneurysms during a 15-year interval. Thirty-day mortality was 11.3%, and permanent SCII developed in 36 patients (4.4%). Among the 348 patients who had intact MEP and SSEP signals at the end of the procedure, 1 patient (0.3%) developed permanent SCII. Among the 283 patients who experienced isolated MEP loss, 274 had intact signals at the end of the procedure, and 8 patients (2.8%) developed permanent SCII. Among the 173 patients who experienced both MEP and SSEP loss, 143 had intact MEPs and 150 had intact SSEPs at the end of the procedure, and 27 patients (15.6%) developed permanent SCII. It was not possible from the data presented to determine whether the patients in the latter 2 groups who developed permanent SCII had absent or intact signals at the end of the procedure, and thus it is not possible to determine the percentage of false-positive cases and the positive predictive value from these 2 groups. There was a substantial prevalence of transient SCII (47of a total of 83 patients). Delayed SCII (permanent or transient) was far more prevalent than immediate SCII (63 vs 20 patients). The authors acknowledge that interpretation of evoked potential signals is operator dependent, requires an experienced neurophysiologist to obtain and interpret the data, and that a learning curve definitely exists. The costs and the cost-effectiveness of the monitoring equipment and personnel required for routine use and interpretation of evoked potential monitoring were not addressed. Substantial modifications in anesthetic technique were required to prevent interference with the SSEP and MEP signals, including the avoidance of neuromuscular blockade. The authors conclude that “SSEP and MEP are both important monitoring measures to predict and prevent spinal cord ischemia during distal aortic repairs.” Their study clearly demonstrates a very strong negative predictive value associated with SSEP and MEP monitoring and confirms the results from an earlier study,4Keyhani K. Miller III, C.C. Estrera A.L. Wegryn T. Sheinbaum R. Safi H.J. Analysis of motor and sensory evoked potentials during thoracic and thoracoabdominal aortic aneurysm repair.J Vasc Surg. 2009; 49: 36-41Abstract Full Text Full Text PDF PubMed Scopus (91) Google Scholar from 2 systematic reviews,5Fok M. Jafarzadeh F. Sancho E. Abello D. Rimmer L. Callum H. et al.Is there any benefit of neuromonitoring during descending and thoracoabdominal aortic aneurysm repair?.Innovations (Phila). 2015; 10: 342-348Crossref PubMed Google Scholar,6Tanaka Y. Kawaguchi M. Noguchi Y. Yoshitani K. Kawamata M. Masui K. et al.Systematic review of motor evoked potentials monitoring during thoracic and thoracoabdominal aortic aneurysm open repair surgery: a diagnostic meta-analysis.J Anesth. 2016; 30: 1037-1050Crossref PubMed Scopus (34) Google Scholar and from 1 multicenter trial,7Yoshitani K. Masui K. Kawaguchi M. Kawamata M. Kakinohana M. Kato S. et al.Clinical utility of intraoperative motor-evoked potential monitoring to prevent postoperative spinal cord injury in thoracic and thoracoabdominal aneurysm repair: an audit of Japanese association of spinal cord protection in aortic surgery database.Anesth Analg. 2018; 126: 763-768Crossref PubMed Scopus (11) Google Scholar all of which demonstrated a low prevalence of SCII if the MEP signals remained or returned to normal during the operative period, with a specificity that exceeded 95%. In the latter studies,5Fok M. Jafarzadeh F. Sancho E. Abello D. Rimmer L. Callum H. et al.Is there any benefit of neuromonitoring during descending and thoracoabdominal aortic aneurysm repair?.Innovations (Phila). 2015; 10: 342-348Crossref PubMed Google Scholar, 6Tanaka Y. Kawaguchi M. Noguchi Y. Yoshitani K. Kawamata M. Masui K. et al.Systematic review of motor evoked potentials monitoring during thoracic and thoracoabdominal aortic aneurysm open repair surgery: a diagnostic meta-analysis.J Anesth. 2016; 30: 1037-1050Crossref PubMed Scopus (34) Google Scholar, 7Yoshitani K. Masui K. Kawaguchi M. Kawamata M. Kakinohana M. Kato S. et al.Clinical utility of intraoperative motor-evoked potential monitoring to prevent postoperative spinal cord injury in thoracic and thoracoabdominal aneurysm repair: an audit of Japanese association of spinal cord protection in aortic surgery database.Anesth Analg. 2018; 126: 763-768Crossref PubMed Scopus (11) Google Scholar however, considerably more variability in the ability to predict the occurrence of permanent SCII was noted when the signals did not return to normal at the end of the procedure. As noted previously, it was not possible in the study of Tanaka and colleagues3Tanaka A. Nguyen H. Dhillon J.S. Nakamura M. Zhou S.-F. Sanhu H.K. et al.Reappraisal of the role of motor and somatosensory evoked potentials during open distal aortic repair.J Thorac Cardiovasc Surg. 2023; 165: 944-953Abstract Full Text Full Text PDF Scopus (2) Google Scholar to determine the positive predictive value of evoked potential monitoring from the data presented. Although the prevalence of permanent SCII in their study was 4.4% overall, it varied widely according to the extent of aorta involved. For the Crawford extent I, II, III, and IV thoracoabdominal aortic aneurysms, the rates of permanent SCII were 3.1%, 9.7%, 12%, and 3.7%, respectively. The authors acknowledge that these rates do not differ appreciably from those reported from other institutions, where identical techniques were used to minimize the risks of SCII, but without evoked potential monitoring.8Coselli J.S. LeMaire S.A. Preventza O. de la Cruz K.I. Cooley D.A. Price M.D. et al.Outcomes of 3309 thoracoabdominal aortic aneurysm repairs.J Thorac Cardiovasc Surg. 2016; 151: 1323-1337Abstract Full Text Full Text PDF PubMed Scopus (384) Google Scholar,9Wongkornrat W. Yamamoto S. Sekine Y. Makoto O. Fujikawa T. Oshima S. et al.Predictors of paraplegia with current thoracoabdominal aortic aneurysm repair.Asian Cardiovasc Thorac Ann. 2015; 23: 406-411Crossref PubMed Scopus (10) Google Scholar The rates also do not differ from those reported from other studies that employed deeper levels of hypothermia, where use of evoked potential monitoring was not feasible.10Fehrenbacher J.W. Siderys H. Terry C. Kuhn J. Corvera J.S. Early and late results of descending thoracic and thoracoabdominal aortic aneurysm open repair with deep hypothermia and circulatory arrest.J Thorac Cardiovasc Surg. 2010; 140: S185-S190Abstract Full Text Full Text PDF Scopus (66) Google Scholar,11Kouchoukos N.T. Kulik A. Haynes M. Castner C.F. Early outcomes after thoracoabdominal aortic aneurysm repair with hypothermic circulatory arrest.Ann Thorac Surg. 2019; 108: 1338-1344Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar Thus, the answer to the question of whether use of evoked potential monitoring prevents permanent SCII remains moot. Tanaka and colleagues are to be commended for undertaking this large, complex, and well-executed study, which provides additional support to the concept that permanent loss of evoked potentials is predictive of immediate and delayed SCII. Unfortunately, it does not resolve the controversy regarding the effectiveness of evoked potential monitoring in reducing the prevalence of permanent SCII. Reappraisal of the role of motor and somatosensory evoked potentials during open distal aortic repairThe Journal of Thoracic and Cardiovascular SurgeryVol. 165Issue 3PreviewIntraoperative motor and somatosensory evoked potentials have been applied to monitor spinal cord ischemia during repair. However, their predictive values remain controversial. The purpose of this study was to evaluate the impact of motor evoked potentials and somatosensory evoked potentials on spinal cord ischemia during open distal aortic repair. Full-Text PDF