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PVSS2. Intraoperative SSEP Monitoring During Carotid Endarterectomy – Is it Enough?

Raghunandan L. Motaganahalli, Richard C. Pennell, Christopher G. Pennell, Vito A. Mantese, Scott G. Westfall, Joseph J. Hurley.
St. Louis University Hospital, St. Johns Mercy Medical Center, St. Louis, Mo.

OBJECTIVES: Somatosensory evoked potential (SSEP) monitoring has been suggested as a highly specific and sensitive method for neuromonitoring during carotid endarterectomy (CEA). We analyze and report the results of SSEP in patients undergoing CEA.

METHODS: This is a retrospective study involving patients undergoing CEA. Over a 6 years period from 2001-2007, we performed CEA on 600 patients with intraoperative SSEP monitoring. The recordings of 50/10 (more than 50% drop in the amplitude or 10% increase in the latency of the SSEP average recordings) were considered abnormal. Data was collected from retrospective review of charts and SSEP recordings of selectively shunted patients.

RESULTS: Results of 600 patients undergoing CEA with SSEP intraoperative neuromonitoring were analyzed. The M: F ratio was 1.4:1. Selective shunts were placed in 8.7% of pts (46/527) based on abnormal SSEP recordings. Prophylactic shunts were placed in 11.9% of patients (73/600). There was no difference in abnormal SSEP recordings between normal and diabetic patients (p=0.064). SSEP changes failed to resolve in 2 patients despite shunting and all these patients had a stroke. In this series there was a 2.0% (11/527) risk of postoperative major/minor strokes with 1.5% 30 days mortality. The Mantel-Haenszel common odds ratio estimate suggests that patients with symptomatic carotid disease and intra operative SSEP changes are 3.75 times more likely to have a stroke. Of the 11 patients with perioperative strokes 6 had normal SSEP findings. However, only 1 of these was felt to be a failure of SSEP to identify ischemia. The remaining stroke patients had technical problems with reconstruction and developed neurologic events after SSEP was completed. Progressive severity of contralateral carotid stenosis resulted in increasing risk of SSEP changes [Table]. Our data suggest that SSEP recordings have a sensitivity of 93.7%, specificity of 33%. The positive predictive value of the SSEP was 99.5%. Patients with normal SSEP findings are very unlikely to have ischemia.

CONCLUSIONS: SSEP is a highly sensitive method for detecting cerebral ischemia. Patients with contralateral carotid occlusion or high-grade stenosis are at high risk for SSEP changes. Diabetes does not have any impact on SSEP recordings. Patients with symptomatic carotid disease and SSEP changes have a higher risk of perioperative stroke.