BACKGROUND: Experience with Intraoperative monitoring using neurophysiological and haemodynamic indices in 500 operations for carotid endarterectomy is reported. METHODS: Transcranial Doppler technique (TCD), electroencephalogram (EEG) and bilateral median somatosensory evoked potentials (SEP) were performed. Latency and amplitude of SEP, spectral analysis of EEG signal and blood flow velocity in the medial cerebral artery (MCA) were continuously measured. FINDINGS: After two consecutive drops of N20/P25 complex of more than 50%, a warning was given, and when the decrease continued, an the alarm raised. Abnormal EEG changes, if any, appeared after a significant decrease in the N20/P25 amplitude. A mean blood flow velocity drop below 40% of the reference value after cross clamping was rated as a significant warning event.A warning as a result of a decrease in N20/P25 amplitude occurred in 80 operations (16.0%), after an spectral edge frequency decrease in 2 cases (0.4%) and after a V(mean) decrease in 21 cases (4.2%). False negative results were experienced in 2 patients (0.4%). A shunt was inserted in 2.8% of the operations. The overall mortality/morbidity rate was 2.4%. CONCLUSION: A decrease of more than 50% in the amplitude of the thalamocortical somatosensory evoked potential complex N20/P25 proved to be the most reliable warning of danger of ischaemia during carotid endarterectomy.

1st Medical Faculty Department of Neurosurgery Charles University Prague Czech Republic