Delayed cerebral ischemia (DCI) is the most important and preventable morbidity cause after subarachnoid hemorrhage (SAH). Therefore, DCI early detection is a major challenge. Yet, neurological examination can be unreliable in poor grade SAH patients. EEG provides information from most superficial cortical area, with ischemia-related changes. This study aims at defining an alpha-theta/delta (AT/D) ratio decrease thresholds to detect DCI.

We used EEG with a montage matching vascular territories (right and left anterior central and posterior) and compared them to follow-up brain imaging. Results 15 SAH patients (Fischer≥3, World Federation of Neurological Surgeons scale ≥4, 9 DCI) were monitored during 6.4 [4-8] days (min=2d, max=13d). AT/D changes could follow three different patterns: (1) prolonged or (2) transient decrease and (3) no decrease or progressive increase. A regional 30% decrease outlasting 3.7h reached 100% sensitivity and 88.9% specificity to detect DCI. Only 22.6% were in a zone of uncertain diagnosis (3.7-8.04h). These prolonged decreases, with a loss of transient changes, started in cortical areas evolving toward DCI, and preceded intracranial changes when available.

Although this study has a small sample size, prolonged AT/D decrease seems to be a reliable biomarker of DCI. Significance cEEG changes are likely to precede cerebral infarction and could be useful at the bedside to detect DCI before irreversible damage.

1. An EEG montage matching vascular territories is relevant to monitor subarachnoid hemorrhage patients. 2. Prolonged alpha-theta/delta ratio (AT/D) decrease starting in one territory seems to be a good biomarker of delayed cerebral ischemia. 3. Other AT/D patterns and EEG changes can complement daily neurological examination.