BT_PO 1.94 Outline the basis of the electroencephalogram

This is the first of three posts on the EEG – 1) the basic physiology, 2) how drugs affect the EEG, and 3) quantitative EEG monitors.

Inferring the state of consciousness by analysing electrical voltages on the surface of the forehead may seem a bit like trying to see who is winning the football by holding a voltmeter up to the TV screen. However, as reversible obliteration of consciousness is our core business, and the electroencephalogram (EEG) is one of the few ways to observe the effect of drugs on the brain, it is important to understand some basics of the EEG, in part so that the various claims made for quantitative EEG devices can be assessed critically.

Useful resources include the 8th Ed of Miller, especially Chapter 17, which is available online from the ANZCA website.

T / F    The frontal EEG is a mixture of electrical signals derived from the cerebral cortex as well as sub-thalamic structures and the limbic system.

T / F     An “activated” EEG means that the amplitude of the EEG waveform is reduced.

T / F    The amplitude of an awake EEG is about the same as the p-wave on a standard ECG.

T / F    The amplitude of the EEG decreases with age.

T / F   “Burst suppression” is defined as periods of electrical activity alternating with periods of isoelectric EEG.

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