Subclinical ischemia verified by somatosensory evoked potential amplitude reduction during carotid endarterectomy: negative effects on cognitive performance

Abstract

Object Although the mechanisms underlying neurocognitive changes after carotid endarterectomy (CEA) are poorly understood, intraoperative ischemia and postoperative hemodynamic changes may play a role. Methods Data from 81 patients who underwent unilateral CEA with routine shunt use for carotid artery stenosis were retrospectively evaluated. These patients underwent neuropsychological examinations (NPEs), including assessment by the Wechsler Adult Intelligence Scale–Third Edition and the Wechsler Memory Scale–Revised before and 6 months after CEA. Results of NPEs were converted into z scores, from which pre- and postoperative cognitive composite scores (CSpre and CSpost) were obtained. The association between the change of CS between pre- and postoperative NPEs (that is, CSpost − CSpre [CSpost – pre]) and various variables was assessed. These latter variables included ischemic or hemodynamic parameters such as 1) intraoperative hypoperfusion detected by somatosensory evoked potential (SSEP) change—that is, an SSEP amplitude reduction more than 50% and longer than 5 minutes (SSEP< 50%, > 5 min); 2) new lesions on postoperative diffusion-weighted imaging studies; and 3) preexisting hemodynamic impairment. Paired t-tests of the NPE scores were performed to determine the net effect of these factors on neurocognitive function at 6 months. Results A significant CSpost – pre decrease was observed in patients with SSEP< 50%, > 5 min when compared with those without SSEP< 50%, > 5 min (−0.225 vs 0.018; p = 0.012). Multiple regression analysis demonstrated that SSEP< 50%, > 5 min independently and negatively correlated with CSpost – pre (p = 0.0020). In the group-rate analysis, postoperative NPE scores were significantly improved relative to preoperative scores. Conclusions Hypoperfusion during cross-clamping, as verified by SSEP amplitude reduction, plays a significant role in the subtle decline in cognition following CEA. However, this detrimental effect was small, and various confounding factors were present. Based on these observations and the group-rate analysis, the authors conclude that successful unilateral CEA with routine shunt use does not adversely affect postoperative cognitive function.