Critical Care EEG Terminology 2021

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@JudiciousUkulele

Study Notes

This terminology is intended for use in all ages except neonates.
The document is mostly compatible with the 2017 multinational revised glossary of terms.
The document utilizes "ictal" to refer to EEG patterns during epileptic seizures, both clinical and electrographic.
"Hz" is used as an abbreviation for "per second" for all periodic or rhythmic patterns.
All voltage measurements in this document are based on peak to trough in a standard 10–20 longitudinal bipolar recording.
The term "consistent" or "consistently" refers to >80% of instances.

Symmetry:
- Describes the voltage and frequencies in relation to each hemisphere.
- Symmetric indicates equal voltage and frequency bilaterally.
- Mild Asymmetry indicates consistent asymmetry in voltage with a 1 Hz frequency asymmetry.
Predominant Background Frequency
- Assesses the frequency band that is most present when the patient is awake or after stimulation.
- Options include: Beta, Alpha, Theta, and Delta.
Posterior Dominant (“Alpha”) Rhythm
- Must be demonstrated to attenuate with eye opening.
- Present if the frequency can be determined precisely.
- Absent if the pattern is not captured.
- Unclear if the presence of the rhythm is ambiguous.
Continuity
- Assesses how continuous the background pattern appears during the recording.
- Continuous indicates the pattern is consistent in the majority of the recording.
- Nearly Continuous indicates that the pattern is continuous but there are occasional periods of attenuation or suppression.
- Intermittent indicates that the pattern is present in more than 50% of the record.
- Suppression/attenuation indicates the pattern is present in less than 50% of the record.

Electrographic seizures (ESz), electrographic status epilepticus (ESE), electroclinical seizures (ECSz), and electroclinical status epilepticus (ECSE) are defined based on the “Salzburg criteria.”
Brief potentially ictal rhythmic discharges (BIRDs) are included based on recent publications.
Ictal-interictal continuum (IIC) has been proposed.
Other definitions include identical bursts, state changes, cyclic alternating pattern of encephalopathy (CAPE), and extreme delta brush (EDB).

A database incorporating the ACNS terminology was developed for clinical and research purposes.
It is available on the ACNS website.
The database has allowed for multicenter investigations into the clinical significance of rhythmic and periodic patterns (RPPs) in critically ill patients.
Patterns including lateralized rhythmic delta activity (LRDA) have been shown to be associated with acute seizures.
The association of several patterns with seizures was defined in a multicenter cohort of almost 5,000 patients.
Studies have shown that several modifiers within the nomenclature have clinically relevant meaning.

The document provides definitions for various EEG patterns and terms.
All definitions are based on extensive discussion and consensus among experts.
Electronic voting was used for issues that did not have complete consensus.
The document includes schematic diagrams of the core features and principles of the patterns.
Supportive EEG examples from 30 cases are available as Supplemental Digital Content.

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