Correlation of Regional Cerebral Blood Flow (rCBF) with EEG Changes During Isoflurane Anesthesia for Carotid Endarterectomy

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Abstract
A prospective evaluation of regional cerebral blood flow (rCBF) (ipsilateral middle cerebral artery distribution) was determined using a 133Xe clearance technique in 31 ASA P.S. II-III patients anesthetized with isoflurane-50% N2O in O2 for carotid endarterectomy. Each patient was monitored with 16-channel EEG throughout anesthesia and surgery. Critical rCBF was defined as that flow below which EEG signs of ischemia occurred. Critical rCBF (T1/2 method of analysis) was < 10 ml .cntdot. 100 g-1 .cntdot. min-1 (mean .+-. SE 5.9 .+-. 1.2) in the six patients in whom transient EEG changes occurred at the time of temporary surgical carotid artery occlusion. No EEG changes occurred with occlusion in the other 25 patients; mean (.+-. SE) occlusion in the other 25 patients; mean (.+-. SE) occlusion rCBF in this group was 18.9 .+-. 1.3 ml .cntdot. 100 g-1 .cntdot. min-1 (P < 0.001). Preocclusion flows were not significantly different in the two groups. Critical rCBF during isoflurane anesthesia was less than that previously determined during halothane anesthesia (18-20 ml .cntdot. 100 g-1 .cntdot. min-1), and is compatible with the effects of isoflurane on CMRO2 and CBF.