Normal EEG waves: Beta (14-30 Hz), Alpha: 8-13, Theta (4-7 Hz), Delta (<3.5 Hz):
The earliest signs of metabolic encephalopathy is a mild slowing of the occipital dominant alpha activity (alpha rhythm) into a theta range. Diffuse fragmentary or sustained theta and delta waves can be seen.
In more advance cases, the alpha rhythm and the normal faster alpha and the frontal beta activity (14-30 Hz) will be lost and diffuse theta delta activity become more prominent and sustained.
With worsening, periods of diffuse amplitude attenuation and generalized rhythmic delta activity (GRDA), often frontally predominant , will be seen. The EEG variability and state transition will be lost, and the EEG becomes unreactive to stimuli (pain).
As encephalopathy worsens, the EEG reaches diffuse burst-suppression pattern and ultimately electrocerebral inactivity.
