SOMATOSENSORY-EVOKED POTENTIAL MONITORING IN CAROTID SURGERY .1. RELATIONSHIPS BETWEEN QUALITATIVE SEP ALTERATIONS AND INTRAOPERATIVE EVENTS

This paper presents the results of intraoperative median nerve SEP mon itoring in 205 successive patients undergoing isolated carotid endarte rectomy (CE) (N = 172) or CE followed by coronary bypass (CBP) and/or vascular replacement (VR) (N = 33). The left and right median nerves w ere alternately stimulated and recordings performed on 4 channels: cer vical, ipsi-and contralateral parietal, and frontal. SEPs were qualita tively rated in terms of mild, moderate, or severe ipsilateral, contra lateral, or bilateral abnormalities. The SEP abnormalities were subdiv ided into 5 categories as a function of their relationships with intra operative events: no alterations (67.3%), early or late SEP alteration s after carotid cross-clamping (15.6%), SEP alterations after a drop i n blood pressure (occurring outside of or within the cross-clamping pe riod) (15.1%), SEP alterations of a most likely embolic origin (2.4%), SEP changes after head positioning (1%), and SEP changes after a modi fication of the anesthetic regimen (1.5%). Only moderate to severe SEP alterations occurring soon after carotid crossclamping justified shun t installation in 16% of the cases. SEP alterations after a drop in bl ood pressure were reversed merely by restoring blood pressure. The neu rological outcome was uneventful in 94.2% of cases. Of the 12 patients who developed neurological sequellae, only one case presented transie nt sequellae after isolated CE without SEP changes white most cases ei ther had undergone combined CE and CBP and/or VR (6 cases) or had pres ented SEP alterations of embolic origin (3 cases). We conclude that ou r system of qualitative rating of SEPs proved very sensitive to intrao perative hemodynamic disturbances or macroembolisms. (C) 1997 Elsevier Science Ireland Ltd.