Standardized Critical Care EEG Terminology PDF

L. J. Hirsch, et al. Standardized Critical Care EEG Terminology FIG. 8. State changes. At least 2 sustained types of...

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 the less alert to more alert/more stimulated state. 4. The 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. 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, regional, and has been used widely to refer to patterns, discharges, seizures, hemispheric patterns. and epilepsies that are not truly generalized. “Generalized” in this c. Bilateral Independent (BI): two independent (and therefore sense has also been used in many studies in the literature related asynchronous) lateralized patterns with one in each hemi- to critical care EEG and in the previous version of this sphere, with both patterns occurring simultaneously (see Supp nomenclature. Thus, it was not changed. EEG 9, Supplemental Digital Content 1, http://links.lww.com/ NOTE: Additional localizing information for Generalized JCNP/A134) (Fig. 17), i.e., two independent patterns occur- patterns: ring at the same time (overlapping in time) rather than i. “Frontally predominant”: Voltage in anterior derivations is sequentially (one starting after the other stops). at least 50% greater than that in posterior derivations on a NOTE: If there are two independent lateralized patterns at common average, transverse bipolar, ipsilateral ear, or different times (e.g., on the left for an hour and then later in the noncephalic referential recording (see Supp EEG 7, record on the right for an hour), these would be LPDs from the Supplemental Digital Content 1, http://links.lww.com/ left and LPDs from the right, but not BIPDs because they are not JCNP/A134). simultaneous. ii. “Occipitally predominant”: Voltage in posterior derivations NOTE: The “I” in “BI” is capitalized because it stands for its is at least 50% greater than in anterior derivations on a own word, “Independent.” common average, transverse bipoloar, ipsilateral ear, or noncephalic referential recording. iii. “Midline predominant”: Voltage in midline derivations is at least 50% greater than in parasagittal derivations on a common average or noncephalic referential recording. FIG. 10. Anterior-posterior (AP) gradient. FIG. 12. Polyspike versus BIRDs versus Highly Epileptiform Bursts. clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 9 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.  L. J. Hirsch, et al. Standardized Critical Care EEG Terminology d. Unilateral Independent (UI): two independent (and therefore asynchronous) periodic (see Supp EEG 10, Supplemental Digital Content 1, http://links.lww.com/JCNP/A134) or rhyth- mic patterns (see Supp EEG 11, Supplemental Digital Content 1, http://links.lww.com/JCNP/A134) in the same hemisphere, with both patterns occurring simultaneously (Fig. 18), i.e., two independent patterns occurring at the same time (overlapping in time) rather than sequentially (one starting after the other stops). NOTE: If there are two independent lateralized patterns at different times (e.g., in the left frontal region for an hour and then later in the record the left temporal region for an hour), these would be two populations of LPDs on the left, but not unilateral independent periodic discharges because they are not simultaneous. NOTE: Focal midline patterns can be deemed in the same hemisphere (ipsilateral) as an independent pattern in either the left or right hemisphere. For example, PDs at 1 Hz in the left hemisphere occurring simultaneously with independent focal midline PDs at 0.5 Hz would still qualify as unilateral FIG. 14. Lateralized Periodic Discharges (LPDs, unilateral). Unilateral: Periodic discharges only seen in one hemisphere (in this independent periodic discharges. case left). e. Multifocal (Mf): at least three independent lateralized patterns, with at least one in each hemisphere, with all three or more patterns Referred to as “Lateralized, bilateral asymmetric.” For occurring simultaneously (see Supp EEG 12, Supplemental Digital example, PDs seen bilaterally and synchronously but consis- Content 1, http://links.lww.com/JCNP/A134) (Fig. 19). tently greater on the left would be referred to as “Left LPDs, bilateral asymmetric” (see Supp EEG 13, Supplemental NOTE: Additional localizing information for Lateralized Digital Content 1, http://links.lww.com/JCNP/A134). patterns: c. “Bilateral asynchronous”: seen bilaterally but clearly and i. Specify unilateral versus bilateral; and if bilateral, whether consistently with a lead-in from the same side (Fig. 16). asymmetric, asynchronous, or both: Referred to as “Lateralized, bilateral asynchronous.” For a. “Unilateral”: seen in only one hemisphere (Fig. 14). Side example, bifrontal LPDs that are consistently earlier on the should be specified. left. Specify the typical time lag between sides. b. “Bilateral asymmetric”: seen bilaterally but clearly and consistently higher amplitude in one hemisphere (Fig. 15). FIG. 15. Lateralized Periodic Discharges (LPDs, bilateral FIG. 13. Generalized Periodic Discharges (GPDs). Generalized: asymmetric). Bilateral asymmetric: Periodic discharges seen Bilateral synchronous and symmetric periodic discharges. In this bilaterally but clearly and consistently (.80% of the time) higher case, the pattern is “frontally predominant.” amplitude over one hemisphere (in this case left). 10 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. FIG. 18. Unilateral Independent Periodic Discharges (UIPDs). In UIPDs, periodic discharges occur in two independent locations simultaneously with both populations within a single hemisphere (in this case left). FIG. 16. Lateralized Periodic Discharges (LPDs, bilateral asynchronous). Bilateral asynchronous: Periodic discharges seen bilaterally but clearly and consistently (.80% of the time) earlier on one side (in this case left). These are not Bilateral Independent i. Specify symmetric versus asymmetric (BI) because the latency between hemispheres is fixed (i.e., they a. “Symmetric”: Approximately equal in both hemispheres or are not independent populations). with no consistent asymmetry. Patterns that are bilateral, independent, and symmetric would be called “Bilateral Independent, symmetric,” or “Multifocal, symmetric.” NOTE: A lateralized pattern can be both “bilateral asym- b. “Asymmetric”: Clearly and consistently more prominent on metric” and “bilateral asynchronous.” one side. Patterns that are bilateral and independent but clearly more prominent on one side would be called ii. Specify the most involved lobe(s) (F, P, T, O, or hemispheric “Bilateral Independent, asymmetric,” or “Multifocal, asym- if more specific localization is not possible). metric,” followed by “L. R” or “R. L.” NOTE: For unilateral independent patterns, the above ii. Specify lobes most involved in both hemispheres (F, P, T, O, should be specified for each pattern separately. or “hemispheric” if more specific localization is not possible). NOTE: Additional localizing information for Bilateral Indepen- dent and Multifocal patterns: FIG. 19. Multifocal Periodic Discharges (MfPDs). In MfPDs, periodic discharges occur in three independent locations FIG. 17. Bilateral Independent Periodic Discharges (BIPDs). In simultaneously with at least one in each hemisphere. If all three BIPDs, lateralized patterns occur in each hemisphere populations occurred within a single hemisphere this would remain asynchronously and at different frequencies. UIPDs. clinicalneurophys.com Journal of Clinical Neurophysiology Volume 38, Number 1, January 2021 11 Copyright © by the American Clinical Neurophysiology Society. Unauthorized reproduction of this article is prohibited.