ACNS Guideline on Standardized Critical Care EEG Terminology (2021 Version) PDF

ACNS GUIDELINE American Clinical Neurophysiology Society’s Standardized Critical Care EEG Ter...

ACNS GUIDELINE American Clinical Neurophysiology Society’s Standardized Critical Care EEG Terminology: 2021 Version Lawrence J. Hirsch,* Michael W.K. Fong,† Markus Leitinger,‡ Suzette M. LaRoche,§ Sandor Beniczky,k Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 Nicholas S. Abend,¶ Jong Woo Lee,# Courtney J. Wusthoff,** Cecil D. Hahn,†† M. Brandon Westover,‡‡ XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 Elizabeth E. Gerard,§§ Susan T. Herman,kk Hiba Arif Haider,§ Gamaleldin Osman,¶¶ Andres Rodriguez-Ruiz,§ Carolina B. Maciel,## Emily J. Gilmore,* Andres Fernandez,*** Eric S. Rosenthal,††† Jan Claassen,‡‡‡ Aatif M. Husain,§§§ Ji Yeoun Yoo,kkk Elson L. So,¶¶¶ Peter W. Kaplan,### Marc R. Nuwer,**** Michel van Putten,†††† Raoul Sutter,‡‡‡‡ Frank W. Drislane,§§§§ Eugen Trinka,‡ and Nicolas Gaspardkkkk * Comprehensive Epilepsy Center, Department of Neurology, Yale University School of Medicine, New Haven, Connecticut, U.S.A.; †Westmead Comprehensive Epilepsy Unit, Westmead Hospital, University of Sydney, Sydney, Australia; ‡Department of Neurology, Christian Doppler Klinik, Paracelsus Medical University, Salzburg, Austria; §Department of Neurology, Emory University School of Medicine, Atlanta, Georgia, U.S.A.; kDepartment of Clinical Neurophysiology, Danish Epilepsy Center, Dianalund and Aarhus University Hospital, Aarhus, Denmark; ¶Departments of Neurology and Pediatrics, The Children’s Hospital of Philadelphia and the Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A.; #Brigham and Women’s Hospital, Boston, Massachusetts, U.S.A.; **Division of Child Neurology, Stanford University, Palo Alto, California, U.S.A.; ††Division of Neurology, The Hospital for Sick Children, and Department of Pediatrics, University of Toronto, Toronto, Canada; ‡‡Neurology Department, Massachusetts General Hospital, Massachusetts, U.S.A.; §§ Comprehensive Epilepsy Center, Department of Neurology, Northwestern University, Chicago, Illinois, U.S.A.; kkBarrow Neurological Institute, Phoenix, Arizona, U.S.A.; ¶¶Department of Neurology, Henry Ford Hospital, Detroit, Michigan, U.S.A.; ##Division of Neurocritical Care, Department of Neurology, University of Florida, Gainesville, Florida, U.S.A.; ***Department of Neurology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, U.S.A.; †††Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, U.S.A.; ‡‡‡Neurocritical Care, Department of Neurology, Columbia University, New York, New York, U.S.A.; §§§Department of Medicine (Neurology), Duke University Medical Center, and Veterans Affairs Medical Center, Durham, North Carolina, U.S.A.; kkkDepartment of Neurology, Icahn School of Medicine at Mount Sinai, New York, New York, U.S.A.; ¶¶¶Division of Epilepsy, Mayo Clinic, Rochester, Minnesota, U.S.A.; ###Department of Neurology, Johns Hopkins University School of Medicine, Johns Hopkins Bayview Medical Center, Baltimore, Maryland, U.S.A.; ****Department of Neurology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, U.S.A.; †††† Medisch Spectrum Twente and University of Twente, Enschede, The Netherlands; ‡‡‡‡Medical Intensive Care Units and Department of Neurology, University Hospital Basel, Basel, Switzerland; §§§§Department of Neurology, Harvard Medical School, and Comprehensive Epilepsy Center, Beth Israel Deaconess Medical Center, Boston, Massachusetts, U.S.A.; and kkkkDepartment of Neurology, Université Libre de Bruxelles, H^ opital Erasme, Brussels, Belgium. (J Clin Neurophysiol 2021;38: 1–29) meetings on several continents, subjected to multiple rounds of testing of interrater reliability, underwent many revisions, and was INTRODUCTION then published as an ACNS guideline in 2013.2 Interrater agreement In the early 2000s, a subcommittee of the American Clinical of the 2012 version (published in early 2013) was very good, with Neurophysiology Society (ACNS) set out to “standardize terminol- almost perfect agreement for seizures, main terms 1 and 2, the 1S ogy of periodic and rhythmic EEG patterns in the critically ill to aid modifier, sharpness, absolute amplitude, frequency, and number of in future research involving such patterns.” The initial proposed phases.3 Agreement was substantial for the 1F and 1R modifiers terminology was published in 2005.1 This was presented at many (66% and 67%) but was only moderate for triphasic morphology L. J. Hirsch received consultation fees from Aquestive, Ceribell, Marinus, Medtronic, Neuropace and UCB; received authorship royalties from Wolters Kluwer and Wiley; and received honoraria for speaking from Neuropace and Natus. S. M. LaRoche received royalties from Demos/Springer Publishing. S. Beniczky is consultant for Brain Sentinel & Epihunter and Philips; speaker for Eisai, UCB, GW Pharma, Natus, BIAL; and received research grants from Brain Sentinel, Philips, Eisai, UCB, GW Pharma, Natus, BIAL, Epihunter, Eurostars (EU), Independent Research Fund Denmark, Filadelfia Research Foundation, Juhl Foundation, Hansen Foundation. N. S. Abend received royalties from Demos; grants from PCORI and Epilepsy Foundation; and an institutional grant from UCB Pharma. J. W. Lee received grants from Bioserenity, Teladoc, Epilepsy Foundation; is co-founder of Soterya Inc; is a board member of the American Clinical Neurophysiology Society; does consulting for Biogen; and is site PI for Engage Therapeutics and NIH/NINDS R01-NS062092. C. J. Wustof does consulting for Persyst and PRA Health Care. C. D. Hahn received grants from Takeda Pharmaceuticals, UCB Pharma, Greenwich Biosciences. M. B. Westover is co-founder of Beacon Biosignals. E. E. Gerard received grants from Greenwich Pharmaceuticals, Xenon Pharmaceuticals, Sunovion, and Sage. S. T. Herman received grants from UCB Pharma, Neuropace, Sage. H. A. Haider receives author royalties from UpToDate and Springer; does consulting for Ceribell, and is on advisory board for Eisai. A. Rodriguez-Ruiz is co-owner of Rodzi LLC which has no relationship to this work. E. J. Gilmore received a grant from UCB Pharma. J. Claassen is a shareholder of iCE Neurosystems and received a grant from McDonnell Foundation. A, M. Husain received grants from UCB Pharma, Jazz Pharma, Biogen Idec; and received payment from Marinus Pharma, Eisai Pharma, Neurelis Pharma, Blackthorn Pharma, Demos/Springer and Wolters Kluwer publishers. J. Y. Yoo received grants from NIH NeuroNEXT, Zimmer Biomet, LVIS; and receives author royalties from Elsevier. P. W. Kaplan receives author royalties from Demos and Wiley publishers; does consulting for Ceribell; and is expert witness qEEG. M. R. Nuwer is a shareholder of Corticare. M. van Putten is co-founder of Clinical Science Systems. R. Sutter received grants from Swiss National Foundation (No 320030_169379), and UCB Pharma. F. W. Drislane received a grant from American Academy of Neurology. E. Trinka discloses fees received from UCB, Eisai, Bial, B€ohringer Ingelheim,Medtronic, Everpharma, GSK, Biogen, Takeda, Liva-Nova, Newbridge, Novartis, Sanofi, Sandoz, Sunovion, GW Pharmaceuticals, Marinus, Arvelle; grants from Austrian Science Fund (FWF), Österreichische Nationalbank, European Union, GSK, Biogen, Eisai, Novartis, Red Bull, Bayer, and UCB; other from Neuroconsult Ges.m.b.H., has been a trial investigator for Eisai, UCB, GSK, Pfitzer. The remaining authors have no funding or conflicts of interest to disclose. Many EEG examples are available online as supplemental digital content for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.clinicalneurophys.com). Address correspondence and reprint requests to Lawrence J. Hirsch, MD, Department of Neurology, Comprehensive Epilepsy Center, Yale University School of Medicine, P.O. box 208018, New Haven, CT 06520, U.S.A.; e-mail: [email protected]. Copyright
2020 by the American Clinical Neurophysiology Society ISSN: 0736-0258/20/3801-0001 DOI 10.1097/WNP.0000000000000806 clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 1 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  L. J. Hirsch, et al. Standardized Critical Care EEG Terminology (58%) and fair for evolution (21%, likely at least partly because of the asynchronous” patterns. Electrographic seizures (ESz), electro- short EEG samples provided).3 The authors concluded that interrater graphic status epilepticus (ESE), electroclinical seizures (ECSz), agreement for most terms in the ACNS critical care EEG terminology and electroclinical status epilepticus (ECSE) have now been was high and that these terms were suitable for multicenter research defined, largely based on the “Salzburg criteria.”11,12 Brief on the clinical significance of these critical care EEG patterns. potentially ictal rhythmic discharges (BIRDs) have been added Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 With the help of infrastructure funding from the American based on recent publications13,14, and a consensus definition of the ictal-interictal continuum (IIC) has been proposed. We also added XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 Epilepsy Society and administrative and website support from the ACNS, a database that incorporated the ACNS terminology definitions of identical bursts,15 state changes, cyclic alternating was developed for clinical and research purposes, tested during pattern of encephalopathy (CAPE), and extreme delta brush routine clinical care in multiple centers,4 and made available at (EDB).16 To facilitate daily use, we are also providing the “ACNS no cost on the ACNS website (https://www.acns.org/research/ Standardized Critical Care EEG Terminology 2021: Condensed critical-care-eeg-monitoring-research-consortium-ccemrc/ Version” (see Supplemental Digital Content, http://links.lww.com/ ccemrc-public-database). This greatly enhanced the ability to JCNP/A149) and the “ACNS Standardized Critical Care EEG complete multicenter investigations. Terminology 2021: Reference Chart” (see Supplemental Digital After the establishment of the standardized terminology and Content, http://links.lww.com/JCNP/A150). Finally, for educational free access to a database incorporating these terms, there have been purposes and conceptual clarity, we provided extensive schematic many investigations into the clinical significance of rhythmic and diagrams (Figures 1–42) of most patterns to quickly demonstrate the periodic patterns (RPPs) in critically ill patients. Patterns such as core features and principles. Supplemental figures include EEG lateralized rhythmic delta activity (LRDA) were found to be highly examples from 30 cases and are available as Supplemental Digital associated with acute seizures,5,6 equivalent to the association found Content at http://links.lww.com/JCNP/A134. with lateralized periodic discharges (LPDs) in one study.5 The association of all the main patterns in the nomenclature with seizures was defined in a multicenter cohort of almost 5,000 patients, with seizure rates highest for LPDs, intermediate for LRDA and METHODS generalized periodic discharges (GPDs), and lowest for generalized All the definitions are based on extensive discussions not rhythmic delta activity (GRDA).6 This and other studies have shown only among the authors of this document but also among many that several of the modifiers within the nomenclature do indeed have others, both live and via email and questionnaires. There was clinically relevant meaning. For example, studies have shown that not always complete consensus on some issues; electronic higher frequency (especially.1.5 Hz), higher prevalence, longer voting (with each voter blinded to the opinion of others for the duration, and having a “plus” modifier are all associated with a first round) was used for most of these issues. We considered higher chance of acute seizures.6,7 On the other hand, whether a additional changes from previous versions or from the pattern was spontaneous or “stimulus-induced” did not seem to have literature such as eliminating the 10-second cutoff for defining a significant effect on its association with seizures.6 In other electrographic seizures but because no clear consensus was investigations, the “triphasic morphology” modifier was investigated reached (it was close to a split decision), this was not changed. blindly with multiple expert reviewers, calling into question its relationship with metabolic encephalopathy and its lack of a relationship with seizures.8,9 For patients with refractory status 2021 ACNS CRITICAL CARE EEG TERMINOLOGY epilepticus treated with anesthetic-induced coma, the presence of “highly epileptiform” bursts suggested that an attempted wean off of CONTENTS anesthetics at that time was much more likely to lead to seizure A. EEG BACKGROUND recurrence than if the bursts were not highly epileptiform.10 Even B. SPORADIC EPILEPTIFORM DISCHARGES long-term outcome seemed to be associated with some modifiers, C. RHYTHMIC AND PERIODIC PATTERNS (RPPs) with a higher risk of later epilepsy found if LPDs were more D. ELECTROGRAPHIC AND ELECTROCLINICAL SEI- prevalent, had longer duration, or had a “plus” modifier.7 ZURES [NEW, 2021] E. BRIEF POTENTIALLY ICTAL RHYTHMIC DIS- CHARGES (BIRDs) [NEW, 2021] CHANGES IN THE 2021 VERSION OF F. ICTAL-INTERICTAL CONTINUUM (IIC) [NEW, 2021] THE TERMINOLOGY G. MINIMUM REPORTING REQUIREMENTS Although the previous version of the terminology was easy to H. OTHER TERMS use, reliable, and valuable for both research and clinical care, new terms and concepts have emerged. In this version, we incorporate General Notes recent research findings, add definitions of several new terms, and NOTE: This terminology is intended to be used at all ages, clarify a few definitions of old terms. Most of the old terms remain excluding neonates, although some terms may not be ideal unchanged, but there have been some important clarifications and for infants. For the neonatal version of the terminology, please corrections (such as the calculation of the number of phases) and see https://www.acns.org/UserFiles/file/The_American_Clinical_ multiple additions. All changes have been summarized in Table 1. Neurophysiology_Society_s.12.pdf.18 One new main term 1 was added (Unilateral Independent), and main NOTE: This terminology is intended for use in the term 2 “Lateralized” was updated to include “bilateral critically ill, although it can be applied in other settings as 2 Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 clinicalneurophys.com Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  Standardized Critical Care EEG Terminology L. J. Hirsch, et al. TABLE 1. ACNS Standardized Critical Care EEG Terminology: Major and Minor Changes Between the 2012 and 2021 Versions Major changes EEG background  “Variability” and “Stage II sleep transients (K-complexes and spindles)” now combined under “State changes”.  Cyclic Alternating Pattern of Encephalopathy (CAPE) (new term: Section A7, page 7) Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4  Identical bursts (new term: Section A4d, page 6) XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 Rhythmic and Periodic Patterns (RPPs: PDs, RDA and SW)  Unilateral Independent (UI) (new Main Term 1 option: Section C1d, page 10)  Lateralized (bilateral asynchronous) (Main Term 1: Section C1b, page 9)  Patterns that consistently begin in one hemisphere and propagate to the other hemisphere can now be included as a lateralized (bilateral asynchronous) pattern.  Frequency  For PDs and SW, typical frequencies.2.5 Hz can only be applied to RPPs ,10 s duration (“very brief” by definition); if PDs or SW have a typical frequency.2.5 Hz and are $ 10 s these would qualify as electrographic seizures (criterion A) and should be referred to as such rather than as PDs or SW.  No RPP in this terminology can have a typical frequency of.4 Hz; if a pattern is. 4 Hz and $ 0.5 s, it would always meet criteria for either BIRDs (if ,10 s) or an electrographic seizure (if $ 10 s) (see definitions below). If ,0.5 s, this would not qualify as any RPP, but might qualify as a polyspike.  Evolution  Evolution of an RPP is now limited to patterns that are #4 Hz AND ,10 s duration. Any.4-Hz RPP with evolution lasting ,10 s would qualify as a definite BIRD (see Section E, page 24). Any RPP with evolution lasting $ 10 s meets criterion B of an electrographic seizure and should be coded as such.  Extreme Delta Brush (EDB) (new term: Section C3i, page 19)  Stimulus-Terminated (new modifier) Electrographic and Electroclinical Seizure Activity  Electrographic seizure (ESz) (new term: Section D1, page 22)  Electrographic status epilepticus (ESE) (new term: Section D2, page 23)  Electroclinical seizure (ECSz) (new term: Section D3, page 24)  Electroclinical status epilepticus (ECSE) (new term: Section D4, page 24)  Possible electroclinical status epilepticus (new term: Section D4b, page 24) Brief Potentially Ictal Rhythmic Discharges (BIRDs) (new term: Section E, page 24) Ictal-Interictal Continuum (IIC) (new term: Section F, page 25) Minor changes EEG background  Predominant background frequency  Beta (.13 Hz) has now been added (rather than only “alpha or faster”)  Continuity  Nearly continuous changed from #10% to 1–9% attenuation/suppression  Burst suppression changed from.50% attenuation/suppression to 50–99%  Suppression/attenuation changed from entirety to.99% of the record  Burst attenuation/suppression  Can now also be described by applying the location descriptions of Main term 1  Highly Epileptiform Bursts  Previously: present if multiple epileptiform discharges are seen within the majority (.50%) of bursts and occur at an average of 1/s or faster OR if a rhythmic, potentially ictal-appearing pattern occurs at 1/s or faster within the majority (.50%) of bursts.  Updated to: present if 2 or more epileptiform discharges (spikes or sharp waves) are seen within the majority (.50%) of bursts and occur at an average of 1 Hz or faster within a single burst (frequency is calculated as the inverse of the typical interpeak latency of consecutive epileptiform discharges within a single burst) OR if a rhythmic, potentially ictal-appearing pattern occurs at 1/s or faster within the majority (.50%) of bursts.  Voltage  High (most or all activity $ 150 mV) has now been added as a category Rhythmic and periodic patterns  Duration:  Intermediate duration changed from 1–4.9 mins to 1–9.9 mins (to match the definition of focal status epilepticus with impaired consciousness by the International League Against Epilepsy).17  Long duration accordingly changed from 5–59 mins to 10–59 mins  Absolute voltage (amplitude)  Medium, changed from 50–199 mV to 50–149 mV  High accordingly changed from $ 200 mV to $ 150 mV  Polarity changed from major modifier to minor modifier well. It is mostly compatible with the 2017 multinational NOTE: Although any finding on EEG can be focal, regional, revised glossary of terms most commonly used by clinical or hemispheric, such as an asymmetry or slowing, and this is a electroencephalographers.19 very important distinction in some circumstances such as clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 3 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  L. J. Hirsch, et al. Standardized Critical Care EEG Terminology epilepsy surgery, all of these are combined within the terms b. Absent. “lateralized” or “asymmetric” in this nomenclature. However, c. Unclear. additional localizing information (e.g., where the pattern is maximal and which lobes are involved) can be provided and can also be applied to several modifiers and sporadic epileptiform Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 discharges. This additional localizing information was built into XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 the freely available Critical Care EEG Monitoring Research Consortium (CCEMRC) database that incorporated the previous version of this nomenclature (https://www.acns.org/research/ critical-care-eeg-monitoring-research-consortium-ccemrc/ ccemrc-public-database).4 A new database is being created with this 2021 nomenclature fully incorporated. NOTE: In this section and throughout the document, the term “ictal” is used to refer to an EEG pattern seen during an epileptic seizure, whether clinical or electrographic-only, as the term is commonly used in EEG literature. NOTE: “Hz” is used as an abbreviation for “per second” for all types of periodic or rhythmic patterns, even when referring to noncontinuous waveforms. NOTE: All voltage measurements in this document are based on peak to trough (not peak to baseline) measurements in a standard 10–20 longitudinal bipolar recording. However, for assessing voltage symmetry, an appropriate referential recording is preferred. NOTE: The term “consistent” or “consistently” refers to.80% of instances (e.g.,.80% of discharges in a periodic pattern,.80% of cycles of a rhythmic pattern, or present.80% of the record for a background pattern). A. EEG BACKGROUND 1. Symmetry a. Symmetric. b. Mild asymmetry (consistent asymmetry in voltage [Fig. 1A] on an appropriate referential recording of ,50% or consistent asymmetry in frequency of 0.5 to 1 Hz [Fig. 1B]). c. Marked asymmetry ( $ 50% voltage or.1 Hz frequency asymmetry [Fig. 1C]). NOTE: When any of the following features (Section A2–A10) are asymmetric, they should be described separately for each hemisphere. 2. Predominant Background Frequency When Most Awake or After Stimulation a. Beta (.13 Hz) b. Alpha. c. Theta. d. Delta. NOTE: If two or three frequency bands are equally prominent, report each one. 3. Posterior Dominant (“Alpha”) Rhythm (must be demonstrated to attenuate with eye opening; wait.1 second after eye closure to determine frequency FIG. 1. A. Symmetric vs mild asymmetry in voltage. B. Symmetric to avoid “alpha squeak”) vs mild asymmetry in frequency. C. Marked asymmetry in voltage a. Present: Specify frequency to the nearest 0.5 Hz. and frequency. 4 Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 clinicalneurophys.com Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  Standardized Critical Care EEG Terminology L. J. Hirsch, et al. Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 FIG. 2. Continuity. Percentages for each category refer to the percentage of the record that is “attenuated” or “suppressed.” How this percentage is derived is demonstrated in Fig. 4, page 6. 4. Continuity (Fig. 2) considered continuous. If.99%, it is considered either a. Continuous suppressed or attenuated, but not burst-attenuation/burst- b. Nearly Continuous: continuous, but with occasional (1–9% suppression or discontinuous. For example, a record with of the record) periods of attenuation or suppression lasting 2 second bursts alternating with 8 seconds of suppression $ 1 second. Describe typical duration of attenuation/ would be burst-suppression with a suppression percent suppression. of 80%. i. Attenuation: periods of lower voltage are $ 10 mV but For burst attenuation/burst suppression patterns only, also ,50% of the higher voltage background. specify the following: ii. Suppression: periods of lower voltage are ,10 mV. i. Localization of bursts: Bursts can be described using the NOTE: If attenuations/suppressions are stimulus-induced, same terms in Main Term 1 that apply to rhythmic and this is referred to as “SI-attenuation” or “SI-suppression.” periodic discharges: generalized (including with shifting NOTE: This voltage cutoff, as with other voltages, differs predominance; see Section C 1a below, page 9), lateralized, from the ACNS neonatal terminology.18 bilateral independent, unilateral independent, or multifocal c. Discontinuous: A pattern of attenuation/suppression alternat- (Fig. 5). ing with higher voltage activity, with 10% to 49% of the ii. Typical duration of bursts and interburst intervals. record consisting of attenuation or suppression. iii. Sharpest component of a typical burst using the sharpness d. Burst attenuation/Burst suppression: A pattern of attenuation/ categories defined under Section C 3e below, page 14. suppression alternating with higher voltage activity, with 50% iv. The presence or absence of “Highly Epileptiform Bursts”: to 99% of the record consisting of attenuation (see Supp EEG present if two or more epileptiform discharges (spikes or 1, Supplemental Digital Content 1, http://links.lww.com/ JCNP/A134) or suppression (see Supp EEG 2, Supplemental Digital Content 1, http://links.lww.com/JCNP/A134). NOTE: The term “suppression-burst” is synonymous with “burst-suppression.” NOTE: Bursts must average $ 0.5 seconds and have at least 4 phases (i.e., at least 3 baseline crossings; see Section C 3d, page 13, for definition of number of phases); if shorter or fewer phases, they should be considered “discharges” (as defined under RPPs, main term 2, see Section C 2a, page 12) (Fig. 3). Bursts within burst-suppression or burst-attenuation can last up to 30 seconds. For nearly continuous, discontinuous, and burst attenuation/ burst suppression patterns, specify: i. Attenuation Percent or Suppression Percent: the percent of the record/epoch that is attenuated or suppressed (Fig. FIG. 3. Discharge vs. Burst. *Phase: an area under the curve on one 4). This can range from 1% to 99%. If ,1%, it is side of the baseline (see Section C 3d, page 13, and Fig. 23, page 13). clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 5 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  L. J. Hirsch, et al. Standardized Critical Care EEG Terminology each stereotyped cluster of 2 or more bursts (Fig. 7B) appears visually similar in all channels in most (.90%) bursts (see Supp EEG 4, Supplemental Digital Content 1, http://links.lww.com/JCNP/A134). e. Suppression/attenuation: entirety or near-entirety (.99%) of the record consists of either suppression (all ,10 mV, as Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 defined above) or low voltage activity (all ,20 mV but not XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 qualifying as suppression). Specify whether attenuated or suppressed. FIG. 4. Attenuation percent or Suppression percent: the percent 5. Reactivity of the record/epoch that is attenuated or suppressed. This can Change in cerebral EEG activity to stimulation: This may range from 1% to 99%. If ,1%, it is considered continuous. If include change in voltage or frequency, including attenuation of.99%, it is considered either suppressed or attenuated, but not activity. Strength and/or nature of stimulus should be noted, and discontinuous. For example, a record with 2 second bursts a standard protocol of testing reactivity with multiple escalating alternating with 8 seconds of suppression, as shown here, would be stimuli is strongly encouraged.20,21 Appearance of muscle Burst-Suppression with a suppression percent of 80%. activity or eye blink artifacts does not qualify as reactive. Categorize as the following: sharp waves) are seen within most (.50%) bursts and occur at an average of 1 Hz or faster within a single burst a. Reactive. (frequency is calculated as the inverse of the typical b. Unreactive. interpeak latency of consecutive epileptiform discharges NOTE: It is suggested that if an EEG is “unreactive” after within a single burst) (see Supp EEG 3, Supplemental one round of stimulation, a second round of standardized noxious Digital Content 1, http://links.lww.com/JCNP/A134) (Fig. stimulation should be performed to confirm the finding and 6A); record typical frequency and location (G, L, BI, UI or should be applied with the patient in their nonstimulated state. If Mf, as defined in RPP Section C1, page 9). Also present if “unreactive” and the patient is on sedatives or paralytics, we a rhythmic, potentially ictal-appearing pattern occurs suggest including this important caveat in the impression. within most (.50%) bursts; record maximum frequency c. SIRPIDs-only: when the only reactivity is stimulus-induced and location if this occurs (Fig. 6B). rhythmic, periodic, or ictal-appearing discharges (SIRPIDs).22 v. The presence or absence of “Identical Bursts”: Present if This includes SI-RDA, SI-PDs, SI-SW, SI-seizures, SI-bursts, the first 0.5 seconds or longer of each burst (Fig. 7A) or of SI-IIC, or SI-BIRDs (see multiple sections below). FIG. 5. Localization of bursts. A. Generalized bursts, shifting predominance based on asynchrony. Symmetric bursts, at times starting on the left and others on the right, but never consistently the same side. This would be an example of generalized bursts, with shifting predominance based on asynchrony (rather than asymmetry, where they would sometimes be of greater amplitude on the left and other times the right). B. Lateralized bursts, bilateral asynchronous. Symmetric bursts consistently starting on the left with a lag before being seen on the right. This is an example of lateralized, bilateral asynchronous bursts. They are not Bilateral Independent (BI) bursts because there is a consistent relationship between the activity between hemispheres, i.e. the patterns are not independent. 6 Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 clinicalneurophys.com Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  Standardized Critical Care EEG Terminology L. J. Hirsch, et al. Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 FIG. 7. A. Identical Bursts. The first 0.5 seconds or longer of each burst are visually similar in all channels (though only 1 channel shown) in most (.90%) bursts. B. Identical Bursts in a Stereotyped Cluster. The first 0.5 seconds or longer of each of 2 or more bursts in a stereotyped cluster are visually similar in all channels (though only 1 channel shown) in most (.90%) bursts. NOTE: The presence of state changes virtually always indicates the presence of reactivity; however, the presence of reactivity does not necessarily indicate the presence of state FIG. 6. A. Highly Epileptiform Bursts. --- dashed lines represent changes because the reactivity may last ,60 seconds. longer duration of suppression; ED epileptiform discharge. B. Highly Epileptiform Bursts. --- dashed lines represent longer duration of 7. Cyclic Alternating Pattern of suppression. Encephalopathy (CAPE) CAPE refers to changes in background patterns (which d. Unclear (typically used when testing may have not been may include RPPs), each lasting at least 10 seconds, and adequate, there was too much artifact to assess the response, or spontaneously alternating between the 2 patterns in a regular there was a hint of a change in cerebral activity but not manner for at least six cycles (but often lasts minutes to definite). hours) (Fig. 9). A cycle refers to the period of time before the e. Unknown (typically used when reactivity was not tested or sequence repeats (i.e., includes both states once). Document patient was maximally alert throughout the EEG epoch). whether seen in the patient’s more awake/stimulated state or less awake state if known. Describe each pattern and typical duration of each pattern. Optional: Describe if this pattern 6. State Changes corresponds with cycling of other functions such as respira- Present if there are at least 2 sustained types of tions, heart rate, blood pressure, movements, muscle artifact, background EEG related to the level of alertness or stimu- and pupil size. lation; each must persist at least 60 seconds to qualify as a “state” (Fig. 8). Stimulation should be able to transition the a. Present. patient from the less alert to more alert/more stimulated state. b. Absent. State changes can also occur spontaneously. The more alert/ c. Unknown/unclear. stimulated pattern is considered the primary reported “back- NOTE: If each pattern of CAPE lasts.60 seconds, this ground” EEG pattern for the patient. Categorize state changes would qualify as the presence of state changes. If CAPE is as the following: always present, cannot be interrupted with stimulation, and at a. Present with normal stage N2 sleep transients (K-complexes least one of the states lasts ,60 seconds, it remains possible for a and spindles) patient to have CAPE and no state changes. b. Present but with abnormal stage N2 sleep transients  Describe both K complexes and spindles separately as the 8. Voltage following: a. High: most or all activity $ 150 mV in longitudinal bipolar with i. Present and normal. standard 10–20 electrodes (measured from peak to trough). ii. Present but abnormal. Specify abnormality (e.g., asym- b. Normal. metry, location, frequency, poorly formed). c. Low: most or all activity ,20 mV in longitudinal bipolar with iii. Absent. standard 10–20 electrodes (measured from peak to trough), but c. Present but without stage N2 sleep transients. not qualifying as suppressed. d. Absent d. Suppressed: all activity ,10 mV. clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 7 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  L. J. Hirsch, et al. Standardized Critical Care EEG Terminology FIG. 8. State changes. At least 2 sustained types of background EEG, where: 1. The background activity is related to level of alertness or stimulation. 2. Each must persist $ 60 seconds to qualify as a “state“. 3. Stimulation should be able to transition the patient from Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 the less alert to more alert/more stimulated state. 4. The XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 more alert/more stimulated state is considered the “reported background” EEG. 5. State changes can also occur spontaneously. STIM ¼ stimulation, Spont. ¼ spontaneous. NOTE: If the background is nearly continuous or discon- tinuous, EEG background voltage refers to the higher voltage B. SPORADIC EPILEPTIFORM DISCHARGES portion. This refers to nonrhythmic and nonperiodic spikes, polyspikes, and sharp waves, as previously defined by Kane et al.19 in the 2017 revised glossary of terms most commonly used by clinical 9. Anterior-Posterior (AP) Gradient electroencephalographers. A “spike” is defined as “a transient, An AP gradient is present if, at any point in the epoch, clearly distinguished from background activity, with pointed peak at there is a clear and persistent (at least 1 continuous minute) a conventional time scale and duration from 20 to ,70 ms,” with anterior to posterior gradient of voltages and frequencies such duration measured at the EEG baseline (Fig. 11). A “sharp wave” is that lower voltage, faster frequencies are seen in anterior defined identically, but with a duration of 70 to 200 ms. A spike or derivations, and higher voltage, slower frequencies are seen in sharp wave is usually diphasic or triphasic, apiculate (i.e., pointed posterior derivations (Fig. 10). A reverse AP gradient is defined peak), asymmetric (typically with a steeper ascending slope than identically but with a posterior to anterior gradient of voltages descending, but can be the opposite), and either followed by a slow and frequencies. wave or associated with some other disruption of the background. A a. Present. “polyspike” refers to 2 or more spikes occurring in a row with no b. Absent. interdischarge interval and lasting ,0.5 seconds (if $ 0.5 seconds, c. Present, but reversed. they would either qualify as BIRDs [see section E below, page 24] or, if alternating with suppression or attenuation, a highly epileptiform burst within burst suppression/attenuation [see section A 4d, page 5] 10. Breach Effect [Fig. 12]). The prevalence of epileptiform discharges (combining Breach effect refers to EEG activity over or nearby a skull spikes, polyspikes and sharp waves) should be categorized as follows: defect and consists of activity of higher amplitude and increased a. Abundant: $ 1 per 10 seconds, but not periodic. sharpness, primarily of faster frequencies, compared with the rest NOTE: It can be helpful to record the estimated average and of the brain, especially compared with the homologous region on maximum number of spikes per 10-second epoch when abundant the opposite side of the head. epileptiform discharges are seen. a. Present (provide location). b. Frequent: $ 1/minute but less than 1 per 10 seconds b. Absent. c. Occasional: $ 1/hour but less than 1/minute c. Unclear. d. Rare: ,1/hour FIG. 9. Cyclic Alternating Pattern of Encephalopathy (CAPE). Changes in EEG background between pattern 1 and pattern 2, where: 1. Each pattern lasts at least 10 seconds, 2. Spontaneously alternates between the two patterns in a regular manner, 3. For at least 6 cycles. 8 Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 clinicalneurophys.com Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  Standardized Critical Care EEG Terminology L. J. Hirsch, et al. C. RHYTHMIC AND PERIODIC PATTERNS (RPPs) All terms consist of two main terms, with modifiers added as appropriate. Main term 1 refers to the localization of the pattern and main term 2 specifies the type of pattern. Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC1y0abggQZXdgGj2MwlZLeI= on 12/22/2024 1. Main Term 1: G, L, BI, UI, or Mf a. Generalized (G): any bilaterally synchronous and symmetric pattern (see Supp EEGs 5 and 6, Supplemental Digital Content 1, http://links.lww.com/JCNP/A134) (Fig. 13), even if it has a restricted field (e.g., bifrontal). NOTE: A pattern that is bilateral with shifting predominance FIG. 11. Sporadic Epileptiform Discharges. based on asymmetry (i.e., amplitude, sometimes higher on left and sometimes right), OR based on asynchrony (i.e., timing, sometimes earlier on the left and sometimes right) but is not iv. “Generalized, not otherwise specified”: Similar voltage in consistently (.80% of the time) lateralized to one side would all regions and not qualifying as any one of the above still be considered “Generalized.” With shifting asynchrony, one three categories. should specify the typical time lag between sides. b. Lateralized (L): unilateral (Fig. 14); OR bilateral but clearly NOTE: Some suggested that a more accurate term would be and consistently higher amplitude in one hemisphere (bilateral “bilateral synchronous,” but this was rejected for several reasons: asymmetric) (see Supp EEG 8, Supplemental Digital Content 1. many lateralized patterns are also bilateral synchronous (see 1, http://links.lww.com/JCNP/A134) (Fig. 15); OR bilateral definition of “lateralized” immediately below); 2. this is more but with a consistent lead-in from the same side (bilateral difficult to abbreviate (2 letters); and 3, the word “generalized” asynchronous) (Fig. 16). This includes focal,