The Alpha Delta Ratio in Subarachnoid Hemorrhage

cEEG protocol from one of the studies on Alpha Delta Ratio in SAH:

  1. start CEEG monitoring after aneurysm secured and within 5 days of onset
  2. use 8 electrodes: international 10–20 system: F4, T4, P4, O2, F3, T3, P3, O1 + 1 ground electrode (Fz) and 1 reference electrode (Cz)
  3. continue EEG while in ICU, or stop when patient develops scalp irritations, or did not tolerate electrodes
  4. for sedated patients, use first EEG epoch at least 2 h off sedation
  5. take regular short (30 min) EEG recordings after ICU discharge
  6. restart cEEG recording if patient readmitted to ICU

Example of changes that occurred as a result of DCI


EEG analysis:

  1.  EEG data filtered between 0.5Hz and 35 Hz, fragmented into epochs of 1h each
  2. of each epoch, 5 consecutive minutes containing least amount of artifacts selected
  3. power spectral densities estimated using Welch’s method from which 12 qEEG features were calculated
  4. Total power calculated for all individual EEG channels represents the power of the isgnal between 1-30 Hz, frequency bands were calculated as a ratio of total power
  5. alpha/delta ratio and alpha-beta/delta-theta ratio (ABDTR) calculated from the frequency bands
  6. spectral edge frequency x – frequency below which x percent of total power of given signal located; SEF75 and SEF90 used as qEEG features
  7. asymmetry of EEG calculated by comparing power of channels on L to the R
  8. Bispectral index (BSI) calculated in the frequency range 1-7Hz (BSI slow) and 7-25 Hz (BSI fast)

Article suggests further studies:

Live qEEG feedback can be compared to clinical performance and more detailed information regarding the gain in therapeutic window can be obtained. Furthermore, if qEEG monitoring and automatic analyses provide a reliable indication of DCI development, a study in which therapeutic interventions are guided by qEEG parameters would be of great interest.


Rots, M. L. et al. ‘Continuous EEG Monitoring For Early Detection Of Delayed Cerebral Ischemia In Subarachnoid Hemorrhage: A Pilot Study’. Neurocritical Care (2015): n. pag. Web. 11 Nov. 2015.

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