Continuous EEG monitoring in patients with subarachnoid hemorrhage.

Patients with subarachnoid hemorrhage (SAH) are at risk for seizures and delayed cerebral ischemia, both of which can be detected with continuous EEG monitoring (cEEG). Ischemia can be detected with EEG at a reversible stage. CEEG may be most useful in patients with poor grade SAH, as the neurological exam is of limited utility in these stuporous or comatose patients. Seizures have been detected in 19% of SAH patients undergoing cEEG, with the vast majority (95%) of these seizures being nonconvulsive and without any detectable clinical correlate. Applying quantitative analysis to the cEEG (relative alpha variability, post-stimulation alpha/delta ratio) allows reliable detection of ischemia from vasospasm, with EEG changes often preceding changes in the clinical exam and other non-continuous monitoring techniques by up to two days. In patients at risk for developing vasospasm, cEEG monitoring, preferably with quantitative EEG analysis, should be started as early as possible and carried out for up to 14 days after the SAH. CEEG findings may lead to therapeutic (e.g., antiepileptic medication, hypertensive therapy, angioplasty) or additional diagnostic interventions such as angiography, CT or MRI.