Quantitative continuous EEG for detecting delayed cerebral ischemia in patients with poor-grade subarachnoid hemorrhage

Quantitative EEG for the Detection of Brain Ischemia

“…Th ese patterns correlated well with CT grades of SAH severity and 40% of patients with abnormal EEG on day 5 had neurodeterioration [47]. As predicted by the EEG's close correlation with CBF and metabolism, raw EEG was capable of detecting developing ischemia up to 78% of the time in one study of poor-grade SAH patients [9].…”

“…Serial neurological exams and imaging are only capable of detecting delayed cerebral ischemia once the damage becomes clinically or radiographically apparent. In this case, EEG may be a useful way to detect and subsequently treat ischemia before the injury becomes irreversible [7][8][9][10].…”

The Utility of EEG, SSEP, and Other Neurophysiologic Tools to Guide Neurocritical Care

“…Fast-Fourier-Transformation power trends assess either the total power in a certain band of frequencies (e.g., total alpha power [108]) or the ratio of power (voltage) in 2 specific frequency bands (e.g., power in the alpha range of frequencies vs power in the delta range of frequencies, i.e., "alpha-delta ratio") [109]. Ratios may adjust for artifacts, which increase power in multiple frequency ranges and magnify the effect of transitions from faster alpha frequencies within health brain tissue to slower delta rhythms following ischemia, transitions to sleep, or in the intra-ictal and post-ictal states.…”

“…Of a 34-patient cohort, 9 who developed DCI had a median ADR decrease of 24%, and ADR decrement more than 10% from baseline during 6 consecutive measures was 100% sensitive and 76% specific for delayed cerebral ischemia. Similarly, a single measurement showing more than 50% decrement from baseline had good sensitivity (89%) and specificity (84%) [109]. Another EEG measure, relative alpha variability, has been shown to have excellent sensitivity for detecting angiographic vasospasm by using its qualitative scale.…”

“…Initial experience with quantitative EEG suggested that total power provides high sensitivity exceeding 90% for ischemia following subarachnoid hemorrhage [108]. Quantitative EEG variables, such as relative alpha variability trend of total power and post-stimulation alphadelta ratio (ADR) may be used as an early warning system to detect slowing and loss of fast activity, reflective of focal ischemia in an early timeframe before it is clinically apparent in SAH patients with predominantly good-or poor-grade SAH [109,110]. In SAH patients with depressed level of arousal or coma, such as Hunt-Hess grade IV or V patients, a decline in ADR during periods of arousal has been associated with the development of delayed cerebral ischemia.…”