American Clinical Neurophysiology Society's Standardized Critical Care EEG Terminology: 2012 version.

Continuous EEG Monitoring is becoming a commonly used tool in assessing brain function in critically ill patients. However, there is no uniformly accepted nomenclature for EEG patterns frequently encountered in these patients such as periodic discharges, fluctuating rhythmic patterns, and combinations thereof. Similarly, there is no consensus on which patterns are associated with ongoing neuronal injury, which patterns need to be treated, or how aggressively to treat them. The first step in addressing these issues is to standardize terminology to allow multicenter research projects and to facilitate communication. To this end, we gathered a group of electroencephalographers with particular expertise or interest in this area in order to develop standardized terminology to be used primarily in the research setting. One of the main goals was to eliminate terms with clinical connotations, intended or not, such as “triphasic waves,” a term that implies a metabolic encephalopathy with no relationship to seizures for many clinicians. We also avoid the use of “ictal,” “interictal” and “epileptiform” for the equivocal patterns that are the primary focus of this report. A standardized method of quantifying interictal discharges is also included for the same reasons, with no attempt to alter the existing definition of epileptiform discharges (sharp waves and spikes [Noachtar et al 1999]). Finally, we suggest here a scheme for categorizing background EEG activity. The revisions proposed here were based on solicited feedback on the initial version of the Report [Hirsch LJ et al 2005], from within and outside this committee and society, including public presentations and discussion at many venues. Interand intraobserver agreement between expert EEG readers using the initial version of the terminology was found to be moderate for major terms but only slight to fair for modifiers.  A second assessment was performed on an interim version after extensive changes were introduced. This assessment showed significant improvement with an inter-rater agreement almost perfect for main terms (k = 0.87, 0.92) and substantial agreement for the modifiers of amplitude (93%) and frequency (80%) (Mani R, et al, 2012). Last, after official posting on the ACNS Website and solicitation of comment from ACNS members and others, additional minor additions and revisions were enacted. To standardize terminology of periodic and rhythmic EEG patterns in the critically ill in order to aid communication and future research involving such patterns. Our goal is to avoid terms with clinical connotations and to define terms thoroughly enough to maximize inter-rater reliability. Not included in this nomenclature: Unequivocal electrographic seizures including the following: Generalized spike-wave discharges at 3/s or faster; and clearly evolving discharges of any type that reach a frequency .4/s, whether focal or generalized. These would still be referred to as electrographic seizures. However, their prevalence, duration, frequency and relation to stimulation should be stated as described below when being used for research purposes.  The following patterns are included in this nomenclature and would not be termed electrographic seizures for research purposes (whether or not these patterns are determined to represent seizures clinically in a given patient): Generalized spike and wave patterns slower than 3/s; and evolving discharges that remain slower than or equal to 4/s. This does not imply that these patterns are not ictal, but simply that they may or may not be. Clinical correlation, including response to treatment, may be necessary to make this determination.  This terminology can be applied to all ages, but is not intended for use in neonates.