Correlation of Continuous EEG Monitoring with [O-15]H2O Positron Emission Tomography Determination of Cerebral Blood Flow during Balloon Test Occlusion of the Internal Carotid Artery

Abstract

The purpose of this paper was to evaluate the utility of continuous electroencephalography (EEG) during balloon test occlusion (BTO) of the internal carotid artery (ICA). Continuous EEG monitoring and [O-15] H2O PET cerebral blood flow (CBF) studies were completed in 34 patients undergoing BTO of the ICA. CBF determinations were obtained as a baseline without carotid occlusion, and following balloon occlusion, with continuous EEG monitoring. Patients were divided into three groups based on clinical and CBF response to BTO. Group I had no clinical signs or symptoms and had a CBF decrease less than 10 ml/l00 g/min ipsilateral to the occlusion. Group II had no symptoms but CBF fell to 35 to 25 ml/l00 g/min on the occluded side. Group III were clinically unable to tolerate occlusion or CBF fell to less than 25 ml/l00 g/min on the occluded side. The results of continuous 21 channel EEG monitoring were assessed at the time of the examination and retrospectively reviewed for changes in the EEG pattern indicative of ischaemia. On the basis of PET CBF, eighteen patients were classified as Group I, four as Group II, and twelve as Group III. EEG evidence of ischaemia was seen in three patients, all members of Group III. Of the three patients, only one patient had clinical signs or symptoms of ischaemia. All four patients in Group II had PET quantitated CBF levels indicating carotid sacrifice should be done with caution or following a presacrifice by-pass procedure, and nine patients in Group III with PET quantitated CBFs below eligibility for carotid sacrifice, were not identified by EEG monitoring. Even when CBF falls below 25 ml/100 g/minute continuous EEG monitoring is insensitive to reduction in perfusion. Reliance upon EEG for detection of cerebral hypoperfusion in interventionl neuroradiological procedures will significantly underestimate ischaemic risk.