EEG Interpretation Guidelines

Basic Setup and Recording Parameters

The American Clinical Neurophysiology Society recommends using the standard 19 electrodes of the 10-20 International System for diagnostic purposes, and four electrodes for monitoring purposes, with a recording duration of 20-30 minutes to capture variations in vigilance levels 1, 2
The American Academy of Neurology suggests including both eyes-closed and eyes-open recordings whenever possible, and considering polygraphic recording to better understand unusual EEG patterns 1
Consistent recording conditions, such as same time of day and similar feeding conditions, should be maintained whenever possible 1

Adequate recording duration is necessary to capture both wakefulness and drowsiness, as recommended by the American Clinical Neurophysiology Society 1

The International Federation of Clinical Neurophysiology defines the dominant frequency as alpha (8-13 Hz), beta (>13 Hz), theta (4-7 Hz), and delta (<4 Hz) 1, 3
The American Heart Association recommends assessing symmetry between hemispheres and anteroposterior gradients, and noting reactivity to eye opening/closing and other stimuli 4

Generalized slowing indicates diffuse encephalopathy, as stated by the American Academy of Neurology 3
Triphasic waves are often seen in metabolic encephalopathies, particularly hepatic, according to the American Association for the Study of Liver Diseases 1, 3
Periodic patterns may suggest specific etiologies, such as herpes encephalitis, as recommended by the Infectious Diseases Society of America 5

The American Academy of Neurology recommends evaluating for generalized slowing, which correlates with severity of encephalopathy 1, 3
In hepatic encephalopathy, triphasic waves and increased theta/delta activity should be looked for, as stated by the American Association for the Study of Liver Diseases 2, 3
Quantitative EEG analysis may improve reliability in assessing encephalopathy severity, according to the American Clinical Neurophysiology Society 1, 3

A continuous or nearly continuous normal-voltage EEG background without periodic discharges or seizures within 72 hours from ROSC suggests good outcome, as recommended by the American Heart Association 4, 6
The American Heart Association suggests avoiding using low-voltage or discontinuous EEG background alone for prognostication, and using the American Clinical Neurophysiology Society (ACNS) terminology to classify EEG patterns 4, 6

Failing to consider medication effects on EEG patterns, as stated by the American Academy of Neurology 1
Using EEG-derived indices alone for prognostication, as recommended by the American Heart Association 4
Not recognizing non-convulsive status epilepticus in encephalopathic patients, according to the American Epilepsy Society 5

Evoked potentials are used for assessment of sensory pathways and cognitive function, as recommended by the American Clinical Neurophysiology Society 1, 7