S72. Case of acute stroke after high-risk carotid surgery: Visual and quantitative EEG analysis

Abstract

EEG monitoring in the intensive care unit (ICU) has multiple potential uses outside of seizure detection by providing a continuous noninvasive assessment of neurologic function. Since the early 1990s, EEG has been widely employed intraoperatively during carotid endarterectomy to evaluate for cerebral ischemia. Its utility in the ICU, however, is contingent on access to frequent review by an expert neurophysiologist. Several studies found that quantitative EEG (QEEG), particularly a decrease in the alpha/delta ratio (ADR), can be sensitive in screening for delayed cerebral ischemia after subarachnoid hemorrhage. QEEG monitoring may be useful in other situations during which monitoring for ischemia is critical. The EEG for this case was reviewed by three neurophysiologists. QEEG analysis was performed retrospectively with Persyst InsightII software. A 56-year-old right-handed man presented with acute expressive aphasia. Imaging revealed a left frontal stroke and >70% left internal carotid artery stenosis. Six weeks later, he underwent left carotid endarterectomy, complicated by a diseased vessel wall necessitating complete ligation of the artery. Post-operative neurologic exam was non-focal. He was sedated and placed on normothermia protocol in the ICU to prevent cerebral infarction. Visual EEG review initially showed gradually increasing intermittent left temporal slowing. Approximately 90 min later, acute persistent left hemispheric attenuation was seen, most prominent over the centro-posterior region, followed by a gradual increase in left hemispheric delta slowing. Subsequent neurologic exam off sedation revealed a new right hemiparesis; brain MRI showed an acute left middle cerebral artery infarct. QEEG showed immediate prominent and persistent decreases in delta, theta, and alpha power, as well as large reductions in the amplitude-integrated EEG (aEEG) over the left hemisphere. There was also a slight decline in beta power over the left. A delayed decrease in the ADR over the left side was seen approximately 20 min later. Visual EEG inspection in this case revealed acute lasting focal left hemispheric attenuation, with subsequent increased slowing after the time of presumed infarct. Interestingly, QEEG analysis showed simultaneous decreases in absolute power values and aEEG prior to change in the ADR. An automatic alarm system monitoring multiple QEEG parameters could therefore be helpful in monitoring for cerebral ischemia in the ICU, particularly when a trained neurophysiologist is not available.