Spectral iEEG markers precede SSEP events during surgery for subarachnoid hemorrhage

During neurosurgical intracranial vascular manipulations, surgeons need early feed-back on the effects of temporary vascular occlusion. In surgical practice, commonly the amplitude of somatosensory evoked potentials (SSEP) is monitored. However, the latency between an ischemic event and the drop of SSEP amplitude may amount to several minutes. Therefore intracranial electroencephalogram (iEEG) is tested for its predictive value.

During surgery in 13 patients, SSEP was recorded simultaneously with iEEG. iEEG was analyzed real-time in the frequency domain. Spectral observables of the iEEG were validated on the basis of SSEP by computing the statistical correlation first for the whole data set, then for salient events occurring in the SSEP in the group of patients, and finally for salient events occurring in single patients.

Placement of subdural strip electrodes was compatible with standard surgical routine. Maximal correlation between time series of iEEG and SSEP was found for relative alpha power, which preceded the drop of SSEP by 7min.

iEEG is feasible during neurosurgical intracranial vascular manipulations. Monitoring relative alpha power detects salient events earlier than SSEP.

Early detection of salient events facilitates early reaction of the surgeon and may thereby aid to further reduce intraoperative morbidity.