Abstracts

RATIONALE: Delayed cerebral ischemia (DCI) due to vasospasm is often not detected by clinical exam in patients with poor grade subarachnoid hemorrhage (SAH; Hunt-Hess grade 4-5). Continuous EEG (cEEG) monitoring may be useful to monitor brain function in comatose SAH patients. The objective of this study was to identify quantitative EEG (qEEG) parameters that are highly sensitive for DCI with reasonable specificity in poor grade SAH patients.
METHODS: From a prospectively recruited cohort of 78 patients with Hunt-Hess grades 4-5 SAH admitted to the Columbia Neurological ICU between 1/2000 and 1/2002, 48 patients were eligible for enrollment in the study protocol and cEEG was performed in 34. DCI was detected by clinical exam or CT, and corroborated with angiography and TCD. CEEG was performed from postoperative day 2 to 8. In each patient 20 artifact-free, one-minute epochs of digital EEG directly following stimulation were analyzed: time 1) 10 epochs prior to DCI or on day 1 in patients without DCI, and time 2) 10 epochs during DCI or on day 4-6. After Fast-Fourier-Transform, 12 qEEG parameters were calculated (Magic Marker Insight, Persyst Inc., Arizona). These were averaged for individual patients for times 1 and 2. We calculated a ratio of change (time 2:time1), and determined medians of these ratios for each patient. To incorporate four recording sites into one model, we used the generalized estimating equations method to compare ratios of change in qEEG parameters in patients with and without DCI. We calculated sensitivity and specificity for changes of qEEG parameters [gt]5% and [gt]10%.
RESULTS: Nine of 34 patients (26%) developed DCI, 2 with silent infarction. Among the investigated qEEG parameters, the alpha delta ratio (alpha power/delta power; ADR) demonstrated the strongest association with developing DCI. The median decrease of ADR for patients with DCI was 24%, compared to a median increase of 3% for patients without DCI (Z=4.0, P[lt]0.0001). Using an ADR cutoff of a [gt]5% decrease, there was an 83% sensitivity and 66% specificity to detect DCI. Using a [gt]10% cutoff, sensitivity was 77% and specificity was 74%. Other parameters associated with DCI included increased delta, increased delta/total, decreased alpha/total, and decreased (alpha+beta)/delta power.
CONCLUSIONS: A decrease in the alpha delta ratio is a sensitive method of detecting DCI, with reasonable specificity. This post-stimulation qEEG parameter may supplement the clinical exam in poor grade SAH patients and may prove useful to detect ischemia from vasospasm.