Comparison of simultaneous electroencephalographic and mental status monitoring during carotid endarterectomy with regional anesthesia.

PURPOSE

This study examines the accuracy of intraoperative electroencephalographic (EEG) monitoring for the detection of cerebral ischemia by comparing EEG with simultaneous mental status evaluation (MSE) during carotid endarterectomy in awake patients.

METHODS

Between 1994 and 1997, 208 consecutive carotid endarterectomies were prospectively evaluated for cerebral function during surgery with simultaneous MSE and EEG monitoring. Regional anesthesia (RA), which consisted of superficial cervical block, was chosen preferentially in 75% of the cases, with general anesthesia (GA) reserved for the patients who did not fulfill the criteria for RA. When available, 8-channel EEG monitoring was performed (59% with RA and 55% with GA).

RESULTS

The EEG was a reliable predictor in comparison with MSE in most but not all cases of cerebral ischemia. Significant neurologic changes were noted using MSE in 4 of 89 patients (4.5%) that were not detected using EEG (false negative results). Conversely, 6 of 89 cases (6.7%) showed unilateral slowing without associated changes in MSE (false positive results). For the awake patients, 21 of 150 cases (14%) showed MSE changes that required a shunt. By contrast, 9 of 32 GA cases (28%) showed EEG changes that would have led to shunting (P = NS). In the RA group, there were no strokes versus 3 of 58 cases (5.2%) with strokes in the GA group. Two of 150 cases (0.1%) had transient ischemic attacks in the RA group. There was 1 myocardial infarction in the GA group; no deaths occurred in this series.

CONCLUSION

EEG monitoring yielded a significant number of false positive (6.7%) and false negative (4.5%) results in the detection of neurologic deficits when compared with MSE in the awake patients. In this series, the preferential use of RA resulted in less shunt use and was possibly associated with a lower stroke rate.