Utility of Motor Evoked Potentials in Open Thoracoabdominal Aortic Repair and Risk Factors Associated with Spinal Cord Ischemia
Roberto Giorgio Aru1, David P Stonko1, Li Ting Tan1, Rebecca A Sorber2, Caitlin W Hicks1, James H Black, III1
1Johns Hopkins University, Baltimore, MD;2University of Washington, Seattle, WA
INTRODUCTION: Paraplegia remains the Achilles’ heel of contemporary open thoracoabdominal aortic aneurysm (TAAA) repair. Intraoperative motor evoked potentials (MEPs) provide real-time neurophysiologic monitoring and act as a surrogate for spinal cord homeostasis. The purpose of this study was to identify the utility of MEPs in TAAA repair in predicting spinal cord ischemia and metrics associated with SCI.
METHODS: Patients who underwent open type 2 or 3 TAAA or completion aortic repair utilizing intraoperative MEP monitoring and sequential aortic clamping were identified between May 2006 and July 2023. Patient demographics, indication for the procedure, procedural details, and outcomes were recorded. Statistical analysis was performed using STATA v.18.0.
RESULTS: Ninety-one patients underwent open type 2 (n=45) and 3 (n=26) TAAA and completion aortic (n=20; open in 15, endovascular in 5) repairs. The cohort was predominantly male (n=54, 59.3%) with a mean age of 52.3±16.7 years. There was a high incidence of connective tissue disorders (n=42, 46.2%), hypertension (n=60, 65.9%), smoking history (n=49, 53.69%), and anticoagulant use (n=21, 20.6%). Operative indications included degenerative (n=31, 34.1%) and dissection-related (n=57, 62.6%) TAAA and dissection-related malperfusion (n=3, 3.3%). Of the 91 patients, partial left heart bypass was often (n=75, 82.4%) utilized for distal aortic perfusion, and moderate hypothermia (n=75, 82.4%) and cerebrospinal fluid drainage (CSFD) (n=85, 93.4%) were common adjuncts. The mean red blood cell transfusion for open repair included type 2 (9.6±6.0 units), type 3 (9.0±6.8 units), and completion (9.4±8.6 units) repairs. Seventy-eight patients had MEP monitoring. MEPs were classified as no change (n=42, 53.9%), reversible change (n=26, 33.3%), irreversible change (n=4, 5.1%), and unreliable (n=6, 7.7%). MEP changes were predominantly bilateral (n=69, 88.5%) and occurred most often during the abdominal aortic segment (n= 22, 73.3%). Thirty-four of 78 patients (43.6%) underwent intercostal reimplantation (IR), and of those 30 patients with MEP changes, IR led to a reversible change in 11 (30.1%). The median number of replaced spinal levels was associated with MEP changes (P=0.013; Figure 1). Permanent paraplegia occurred in 4 (4.9%), with 2 (2.5%) immediate and 2 (2.5%) delayed onsets; postoperative shock was contributory in the later 2 patients. MEPs demonstrated high negative predictive value (86.1%) but poor sensitivity (53.9%), specificity (61.7%), and positive predictive value (23.3%) in predicting SCI. The SCI rate increased with greater than 6 replaced spinal levels and was most prevalent in completion aortic repairs (Figure 2). Overall, in-hospitality mortality occurred in 4 (4.4%).
CONCLUSIONS: Intraoperative MEP changes are not specific or sensitive for SCI. The number of replaced spinal levels and previous aortic repair should guide intraoperative neuroprotective measures including IR and CFSD and should take precedence over MEP monitoring.
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