(Medscape article by David Crippen)
Modern processed EEG sorts data into recognizable patterns, including:
- Symmetry — asymmetrical patterns can indicate diminished perfusion to one hemisphere, cerebral embolism, or thrombosis.
- Amplitude — the strength of brain wave vectors. Decreased amplitude suggests commensurate brain activity.
- Frequency — the distribution of vectors throughout all frequency bands. Lower frequencies suggest increasing somnolence.
- Spectral Edge — the Activity Edge. Significant dips in one hemisphere compared with the other suggest focal brain ischemia.
The principle wave seen in normal wakefulness is the alpha rhythm containing waves of 8 to 12 Hz and is very responsive to changing mental activity, increasing with excitement and decreasing with tranquility. Beta rhythm frequently occurs in the prefrontal regions and is indicative of the initial euphoric, anxiolytic, and amnesic stage of sedation. Both theta and delta waves are frequently seen normally during sleep. The administration of neurotransmitter active medications, such as narcotics and benzodiazepines, produce characteristic changes in the patterns of brain waves that are easily interpretable on the cerebral function monitor.
use V5 as your second lead as it is most sensitive for ischemia (75% the sens of 12 lead) (London et al. Anesthesiology 1988;69:232)) V4 is probably as good
Initial study did not show benefit in monitoring ED intubated patients (The American Journal of Emergency Medicine Volume 22, Issue 2 , March 2004, Pages 76-82)
100 Awake 80 Sedated 60 General anesthesia 40 Deep hypnosis 20 Burst suppression 1 Flat line
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