Bilateral BIS Study

Subarachnoid hemorrhage (SAH) is a prevalent and morbid condition (45%-30 day mortality).
One of the major causes of reduced cerebral blood flow (CBF) after initial SAH is cerebral
vasospasm. Early treatment of cerebral vasospasm (< 2 hr) is necessary for improved
neurologic outcome. Hence, there is significant interest in development of a monitor. The
most common bedside diagnostic tool is Transcranial Doppler (TCD) which is controversial
given its low sensitivity and specificity. TCD is not a continuous monitor and is user
dependent. Many centers rely on Cerebral Angiography for diagnosis of vasospasm; however
angiographic spasm does not correlate with outcome. EEG can detect changes in cerebral blood
flow which precede clinical decline but is technically difficult to perform and not
practical for continuous monitoring.

Processed EEG monitors have become somewhat popular in the operating setting for assessment
of depth of anesthesia. The recent introduction of bilateral 4 channel disposable probes
presents to opportunity to use EEG as a non-invasive continuous monitor for vasospasm. We
propose a prospective observational study to assess real time changes in raw and processed
EEG which we will correlate with clinical and radiologic evidence of vasospasm. Our primary
clinical endpoint will be the determination of delayed cerebral ischemia. This modality
could prove to be a significant clinical advantage for patients suffering from SAH.