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Median Nerve Somatosensory Evoked Potential Monitoring During Carotid Endarterectomy: Does Reference Choice Matter?

Fried, Stephen J.*; Smith, Diane M.*; Legatt, Alan D.*,†

Journal of Clinical Neurophysiology: February 2014 - Volume 31 - Issue 1 - p 55–57
doi: 10.1097/WNP.0000000000000024
Original Research

Summary: Median nerve somatosensory evoked potential monitoring is commonly used during carotid endarterectomy to permit selective shunting in only those patients who are determined to have inadequate collateral flow after carotid cross-clamping. The N20 component is recorded from the CPc (contralateral centroparietal) electrode; either CPi (ipsilateral centroparietal) or Fpz (forehead) can be used as the reference. Because of the distribution of the subcortically generated N18 component, the CPc-Fpz derivation might record both the N20 and the N18 components and might therefore inadequately detect hemispheric ischemia after carotid cross-clamping. Somatosensory evoked potentials recorded were compared using these 2 derivations during 38 carotid endarterectomies to assess their ability to detect neurophysiologic changes after carotid cross-clamping. Although, as expected, the baseline N20 component was significantly larger when recorded with the CPc-Fpz derivation than with the CPc-CPi derivation (3.1 vs. 2.4 μV in the hemisphere ipsilateral to the clamped carotid, P < 0.001), there was no significant difference in the postclamp amplitude decline between the 2 derivations (8.7% vs. 8.6%, P = 0.82). It is concluded that CPc-Fpz is an acceptable derivation for recording postclamp hemispheric somatosensory evoked potential changes during carotid endarterectomy and may be advantageous because it provides a larger amplitude somatosensory evoked potential than the CPc–CPi derivation.

Departments of *Neurology and

Neuroscience, Montefiore Medical Center and the Albert Einstein College of Medicine, Bronx, New York, U.S.A.

Address correspondence and reprint requests to Alan D. Legatt, Department of Neurology, Montefiore Medical Center, 111 East 210 Street, Bronx, NY 10467, U.S.A.; e-mail:

This study was presented at the 2013 annual meeting of the American Clinical Neurophysiology Society.

© 2014 by the American Clinical Neurophysiology Society