THE RELIABILITY OF QUANTITATIVE ELECTROENCEPHALOGRAPHY AS AN INDICATOR OF CEREBRAL-ISCHEMIA

The electroencephalogram (EEG) has been used to detect episodes of cer ebralischemia during various surgical procedures. Recently, computeriz ed systems for recording and interpreting the quantitative EEG (QEEG) have been used by anesthesiologists because of their ease of applicati on, clarity of display, and reported ability to identify ischemic EEG changes. However, the extent to which automated techniques of QEEG int erpretation reliably differentiate cerebral ischemia from the confound ing effects of anesthetics and other sources of ''artifact'' is not co mpletely established. In this study, EEGs were recorded before and aft er defibrillator testing in patients undergoing implantable cardiovert er defibrillator (ICD) placement and during analogous time periods in control patients undergoing abdominal surgery. EEGs were subjected to standard visual inspection by an experienced electroencephalographer a nd QEEG analysis with a commercially available system was used for aut omated EEG interpretation in order to evaluate the reliability of this quantitative technique. The CIMON technique identified episodes which met previously defined criteria for QEEG cerebral dysfunction and isc hemic pattern in both groups, despite the presumed absence of cerebral ischemia in the control patients. Since there was no evidence of cere bral. ischemia in the raw EEGs of either the ICD patients or the contr ols, these QEEG changes were not confirmed by conventional techniques of EEG interpretation. Our results suggest that caution is warranted w hen using automated systems for intraoperative interpretation of EEG.