ICU EEG: ICU EEG: Prognosis in AdultsPrognosis in Adults
Susan T. Herman, MDSusan T. Herman, MD
Assistant Professor of NeurologyAssistant Professor of Neurology
Beth Israel Deaconess Medical CenterBeth Israel Deaconess Medical Center
Harvard Medical SchoolHarvard Medical School
Boston, MABoston, MA
DisclosuresDisclosures
None relevant to this presentationNone relevant to this presentation Scientific Advisory BoardScientific Advisory Board
Eisai Inc.Eisai Inc. Biotie, Inc.Biotie, Inc.
ResearchResearch UCB PharmaUCB Pharma Acorda TherapeuticsAcorda Therapeutics Epilepsy Therapy Development ProjectEpilepsy Therapy Development Project Sage PharmaceuticalsSage Pharmaceuticals NeuroPace, Inc.NeuroPace, Inc. PfizerPfizer
Utility of EEG in Critically IllUtility of EEG in Critically Ill
Objectively measure severity of alteration in Objectively measure severity of alteration in consciousnessconsciousness
Assess neurologic function in patients who are Assess neurologic function in patients who are pharmacologically paralyzedpharmacologically paralyzed
Narrow the differential diagnostic possibilities when Narrow the differential diagnostic possibilities when combined with appropriate clinical informationcombined with appropriate clinical information
Determine if nonconvulsive seizures are cause of altered Determine if nonconvulsive seizures are cause of altered consciousness and assess response to treatmentconsciousness and assess response to treatment
Follow progression / improvement with serial studiesFollow progression / improvement with serial studies Provide prognostic informationProvide prognostic information Confirm the diagnosis of brain deathConfirm the diagnosis of brain death
Diffuse EtiologiesDiffuse Etiologies
Metabolic, toxic, infectious encephalopathiesMetabolic, toxic, infectious encephalopathies Grade or degree of abnormalities correlates fairly well Grade or degree of abnormalities correlates fairly well
with clinical statuswith clinical status EEG changes may precede or lag clinical changesEEG changes may precede or lag clinical changes Serial studies may be usefulSerial studies may be useful
Etiology often plays larger role than EEG patternEtiology often plays larger role than EEG pattern
Diffuse EtiologiesDiffuse Etiologies Slowing of posterior dominant rhythmSlowing of posterior dominant rhythm Diffuse thetaDiffuse theta Diffuse polymorphic theta and delta Diffuse polymorphic theta and delta
Loss of faster frequencies and sleep transientsLoss of faster frequencies and sleep transients Abnormal arousalsAbnormal arousals Intermittent rhythmic delta activityIntermittent rhythmic delta activity
Continuous diffuse high amplitude polymorphic deltaContinuous diffuse high amplitude polymorphic delta Continuous diffuse low voltage monomorphic deltaContinuous diffuse low voltage monomorphic delta Burst suppressionBurst suppression Low voltage (<20 Low voltage (<20 μμV) unreactive deltaV) unreactive delta Electrocerebral inactivityElectrocerebral inactivity
GOODGOOD
BADBAD
Classification SystemClassification SystemGr Synek Scollo-Lavizzari Young
I Regular alpha, some theta
Normal alpha Delta-theta > 50% of record
II Predominant theta Alpha, theta/delta Triphasic waves
III Widespread delta, spindle coma
Theta/delta, no alpha
Burst suppression
IV Burst-suppression, alpha coma, theta coma, delta coma
≤ 20 μV
Delta, low voltage; burst-suppression, PEDs, alpha coma
Alpha / theta / spindle coma, unreactive
V ECI ≤ 2 μV Very low to ECI Epileptiform activity
VI Suppression ≤ 10μV
Synek VM. J Clin Neurophysiol. 1988; 5: 161-74Scollo-Lavizzari G, et al. Eur Neurol. 1987; 26: 161-70 Young GB, et al. Can J Neurol Sci 1997;24:320-325
Synek: Prediction of Outcome Synek: Prediction of Outcome after Cardiac Arrestafter Cardiac Arrest
Good OutcomeGood Outcome Grade 1 Grade 1 48/61 48/61 79%79% Grade 2 Grade 2 45/88 45/88 51%51% Grade 3 Grade 3 11/43 11/43 26%26% Grade 4 Grade 4 0/138 0/138 0%0% Grade 5 Grade 5 0/70 0/70 0%0%
Severe Diffuse Slowing & Attenuation
Fp1-F3
F3-C3
C3-P3
P3-O1
Fp2-F4
F4-C4
C4-P4
P4-O2
Fp1-F7
F7-T 3
T 3-T 5
T 5-O1
Fp2-F8
F8-T 4
T 4-T 6
T 6-O2
Fz-Cz
Cz-Pz
LUC
R LC
E KG
Comment100 uV
1 sec
Burst Suppression: Barbiturate-Induced
Fp1-F3
F3-C3
C3-P3
P3-O1
Fp2-F4
F4-C4
C4-P4
P4-O2
Fp1-F7
F7-T 3
T 3-T 5
T 5-O1
Fp2-F8
F8-T 4
T 4-T 6
T 6-O2
Fz-Cz
Cz-Pz
E KG
Comment75 uV
5 sec
Electrocerebral Inactivity, ECI Montage
Fp1-C3
C3-O1
Fp1-T 3
T 3-O1
Fp2-C4
C4-O2
Fp2-T 4
F3-P3
Fz-Pz
F4-P4
F7-Fz
Fz-F8
T 3-Cz
Cz-T 4
T 5-Pz
Pz-T 6
LUC
R LC
E KG
Comment 30 uV
1 sec
2 uV/mm
Focal Structural EtiologiesFocal Structural Etiologies
Cause coma from herniation and compression/distortion Cause coma from herniation and compression/distortion of brainstem and diencephalonof brainstem and diencephalon
Focal asymmetriesFocal asymmetries Polymorphic delta activity: Subcortical white matterPolymorphic delta activity: Subcortical white matter Attenuation of faster frequencies: CortexAttenuation of faster frequencies: Cortex Intermittent rhythmic delta activity: Deep gray matter Intermittent rhythmic delta activity: Deep gray matter
structuresstructures May not be clear which hemisphere is more severely May not be clear which hemisphere is more severely
affected affected Slower frequencies and lower voltagesSlower frequencies and lower voltages
Other EtiologiesOther Etiologies
Brainstem lesionsBrainstem lesions Exception to relationship between EEG and clinical Exception to relationship between EEG and clinical
examexam Patient may be deeply comatosePatient may be deeply comatose Cortex (and therefore EEG) may be relatively Cortex (and therefore EEG) may be relatively
unaffectedunaffected Locked-in syndromeLocked-in syndrome
Psychogenic coma, catatoniaPsychogenic coma, catatonia EEG is normalEEG is normal
ReactivityReactivity
EEG change in response to sensory stimulationEEG change in response to sensory stimulation AuditoryAuditory VisualVisual SomatosensorySomatosensory
Light comaLight coma Generalized high voltage delta burstsGeneralized high voltage delta bursts
Deeper comaDeeper coma Diffuse attenuationDiffuse attenuation
Deep comaDeep coma No reactivity; poorer prognosisNo reactivity; poorer prognosis
Specific Coma Specific Coma PatternsPatterns
Alpha ComaAlpha Coma
Diffuse alpha frequency activity, 8-13HzDiffuse alpha frequency activity, 8-13Hz Often frontally dominantOften frontally dominant InvariantInvariant UnreactiveUnreactive
Transient pattern, evolves to other patternsTransient pattern, evolves to other patterns EtiologyEtiology
AnoxiaAnoxia Brainstem strokesBrainstem strokes Traumatic brain injuryTraumatic brain injury Drug intoxication (benzodiazepines, tricyclic Drug intoxication (benzodiazepines, tricyclic
antidepressants)antidepressants)
Alpha Coma and PrognosisAlpha Coma and Prognosis
Meta-analysis, 335 casesMeta-analysis, 335 cases Etiology predicts outcomeEtiology predicts outcome
Etiology Mortality
Anoxia 88%
Brainstem infarct 90%
Drug intoxication 8%
Kaplan PW, et al. Clin Neurophysiol. 1999; 110: 205-13
Beta ComaBeta Coma
High amplitude (>30 High amplitude (>30 μμV) diffuse 12-16 Hz activityV) diffuse 12-16 Hz activity Often frontally maximalOften frontally maximal UnreactiveUnreactive
EtiologiesEtiologies Drug intoxicationDrug intoxication AnesthesiaAnesthesia
Prognosis usually determined by etiology rather than Prognosis usually determined by etiology rather than EEG patternEEG pattern
Diffuse Beta, Barbiturate-Induced
Fp1-F3
F3-C3
C3-P3
P3-O1
Fp2-F4
F4-C4
C4-P4
P4-O2
Fp1-F7
F7-T 3
T 3-T 5
T 5-O1
Fp2-F8
F8-T 4
T 4-T 6
T 6-O2
Fz-Cz
Cz-Pz
LUC
R LC
E KG
Comment 100 uV1 sec
Spindle ComaSpindle Coma
Diffuse exaggerated 12-14 Hz sleep spindlesDiffuse exaggerated 12-14 Hz sleep spindles Resembles stage 2 or 3 (N2 or N3) sleepResembles stage 2 or 3 (N2 or N3) sleep
May show some stage changes (vertex waves, K May show some stage changes (vertex waves, K complexes)complexes)
No REMNo REM Little or no reactivity to external stimuliLittle or no reactivity to external stimuli
EtiologiesEtiologies Traumatic brain injuryTraumatic brain injury AnoxiaAnoxia Brainstem lesionsBrainstem lesions Drug intoxicationDrug intoxication
Spindle Coma and PrognosisSpindle Coma and Prognosis
Etiology plays a roleEtiology plays a role Overall better prognosis than alpha coma, mortality 23%Overall better prognosis than alpha coma, mortality 23% Presence of normal sleep tranisents suggests that cortex Presence of normal sleep tranisents suggests that cortex
and diencephalon are more intactand diencephalon are more intact
Kaplan PW, et al. Clin Neurophysiol. 2000; 111: 584-90
Etiology Mortality
Structural / brainstem 73%
Hypoxia 33%
Trauma 15%
Drug intoxication 0%
Subarachnoid HemorrhageSubarachnoid Hemorrhage
116 / 756 SAH patients with CEEG and 3 mo mRS116 / 756 SAH patients with CEEG and 3 mo mRS 88% poor grade SAH (Hunt & Hess ≥ 3)88% poor grade SAH (Hunt & Hess ≥ 3) Overall 3 month outcomeOverall 3 month outcome
69% moderate-severely disabled or dead69% moderate-severely disabled or dead 34% dead34% dead
Multivariate analysisMultivariate analysis Poor admission Hunt & Hess grade (OR 7.0)Poor admission Hunt & Hess grade (OR 7.0) Older age (OR 1.0 per year > 65)Older age (OR 1.0 per year > 65) Intraventricular hemorrhage (OR 2.6)Intraventricular hemorrhage (OR 2.6) No effect of delayed cerebral ischemiaNo effect of delayed cerebral ischemia
Claassen J et al. Neurocrit Care 2006;4:103-112Claassen J et al. Neurocrit Care 2006;4:103-112Dennis LJ et al.. Neurosurgery 2002;51:1136-1143Dennis LJ et al.. Neurosurgery 2002;51:1136-1143
CEEG Risk Factors in SAHCEEG Risk Factors in SAH
Claassen J et al. Neurocrit Care 2006;4:103-112Claassen J et al. Neurocrit Care 2006;4:103-112Dennis LJ et al.. Neurosurgery 2002;51:1136-1143Dennis LJ et al.. Neurosurgery 2002;51:1136-1143
EEG Finding Poor outcome
With RF (%)
Poor outcome Without RF (%)
OR 95% CI
Lateralized periodic discharges 91 66 18.8 1.6 - 214.6
Any periodic discharges 90 63 9.0 1.7 - 49.0
Absent sleep, 1st 24 hrs 74 29 10.4 1.4 - 78.1
Absent sleep, entire EEG 89 47 4.3 1.1 - 17.2
Absent reactivity, n = 9 * 100 0 - -
NCSE within 24 hrs, n = 4 * 100 0 - -
NCSE, entire EEG, n = 12 92 8 - -
GPEDs or BiPLEDs, n = 17 * 100 0 - -
* = Specificity and PPV for poor outcome = 100
Intracerebral HemorrhageIntracerebral Hemorrhage
Predictors of poor outcomePredictors of poor outcome Generalized periodic dischargesGeneralized periodic discharges Lateralized periodic dischargesLateralized periodic discharges Stimulus-induced rhythmic, periodic, or ictal Stimulus-induced rhythmic, periodic, or ictal
discharges (SIRPIDs)discharges (SIRPIDs)
Claassen J et al. Neurology 2007;69:1356-1365Claassen J et al. Neurology 2007;69:1356-1365Vespa PM et al. Neurology 2003;60:1441-1446Vespa PM et al. Neurology 2003;60:1441-1446
Cardiac ArrestCardiac Arrest
Therapeutic hypothermiaTherapeutic hypothermia 4 randomized clinical trials4 randomized clinical trials Comatose patients within 6 hrs of arrestComatose patients within 6 hrs of arrest Ventricular fibrillation or pulseless ventricular Ventricular fibrillation or pulseless ventricular
tachycardiatachycardia Mild TH (32-34º C) for 24 hrsMild TH (32-34º C) for 24 hrs Decreased mortality by 20%Decreased mortality by 20% Decreased poor neurologic outcome by 27%Decreased poor neurologic outcome by 27%
Cheung KW et al. Can J Emergency Med. 2006;8:329-337
Cardiac ArrestCardiac Arrest
AAN Practice Parameter: Prediction of outcome in AAN Practice Parameter: Prediction of outcome in comatose survivors after cardiopulmonary resuscitationcomatose survivors after cardiopulmonary resuscitation
Clinical factor Timing Level
Absent pupillary response 3 days A
Absent corneal reflexes 3 days A
Absent motor responses 3 days A
Myoclonic status epilepticus 24 hrs B
Serum NSE > 33µg/L 1-3 days B
Bilateral absent cortical SSEP 3 days B
Wijdicks EF et a;. Neurology 2006;67:203-210Wijdicks EF et a;. Neurology 2006;67:203-210
Cardiac ArrestCardiac Arrest
AAN Practice Parameter: Prediction of outcome in AAN Practice Parameter: Prediction of outcome in comatose survivors after cardiopulmonary resuscitationcomatose survivors after cardiopulmonary resuscitation
EEG finding Timing Level
Generalized suppression ≤ 20µV Any C
Burst-suppression Any C
GPEDs on flat background Any C
Wijdicks EF et a;. Neurology 2006;67:203-210Wijdicks EF et a;. Neurology 2006;67:203-210
Predictors of Poor Outcome: No THPredictors of Poor Outcome: No TH
Myoclonic status epilepticusMyoclonic status epilepticus EEG usually shows burst suppression and/or GPDsEEG usually shows burst suppression and/or GPDs Rare (<5%) with good cognitive outcomeRare (<5%) with good cognitive outcome
Usually treated with high-dose cIV-AEDsUsually treated with high-dose cIV-AEDs Preserved brainstem reflexesPreserved brainstem reflexes Intact cortical SSEP responsesIntact cortical SSEP responses Reactive EEG backgroundReactive EEG background
Predictors of Poor Outcome: No THPredictors of Poor Outcome: No TH
Background EEGBackground EEG Burst-suppressionBurst-suppression DiscontinuityDiscontinuity Generalized voltage attenuation (< 20µV)Generalized voltage attenuation (< 20µV) Alpha / theta / spindle coma without reactivityAlpha / theta / spindle coma without reactivity
Lack of reactivityLack of reactivity Periodic dischargesPeriodic discharges
Generalized periodic discharges on attenuated Generalized periodic discharges on attenuated backgroundbackground
EEG after Cardiac Arrest: No EEG after Cardiac Arrest: No THTH
Sensitivity 94%Sensitivity 94% Specificity 63%Specificity 63%
4 patients with malignant recovered awareness4 patients with malignant recovered awareness
Benign Malignant
Delta / theta > 50% of recording, with or without reactivity
Triphasic waves
Burst-suppression, with or without epileptiform activity
Alpha / theta / spindle coma, without reactivity
Generalized suppressioin
Thenayan EA et al. J Crit Care 2010;25:300-304Thenayan EA et al. J Crit Care 2010;25:300-304
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: No THCardiac Arrest: No TH
Meta-analysis of 50 studiesMeta-analysis of 50 studies 2828 adult patients, comatose after cardiac arrest2828 adult patients, comatose after cardiac arrest Outcomes assessed by Cerebral Performance Category Outcomes assessed by Cerebral Performance Category
(CPC)(CPC) CPC 4-5 vs. 1-3CPC 4-5 vs. 1-3 CPC 3-5 vs. 1-2CPC 3-5 vs. 1-2 Variable timing: hospital discharge to 12 mosVariable timing: hospital discharge to 12 mos
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac arrest: A neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 1: Patients not treated with systematic review and meta-analysis. Part 1: Patients not treated with therapeutic hypothermia. Resuscitation 2013.therapeutic hypothermia. Resuscitation 2013.
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: No THCardiac Arrest: No TH
Finding Timing Sensitivity FPR 95% CI
Quality
Myoclonus, n=471 24-48 hrs 9 0 0-3 Low
Bilateral absent SSEP, n = 293
24-72 hrs 45-46% 0 0-9 Low
Absent pupillary response, n = 382
72 hrs 18 0 0-8 Low
NSE, S-100B Variable -- -- Very low
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac arrest: A neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 1: Patients not treated with systematic review and meta-analysis. Part 1: Patients not treated with therapeutic hypothermia. Resuscitation 2013.therapeutic hypothermia. Resuscitation 2013.
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: No THCardiac Arrest: No TH
EEG Finding Timing Sensitivity FPR 95% CI
Quality
Grade III-V (Edgren), n=46
24 hrs 36 0 0-22 Very low
Grade IV-V (Synek), n=40
≤ 48 hrs 42 0 0-19 Very low
Grade IV-V (Bassetti), n=59
≤ 72 hrs 42 0 0-24 Very low
Low voltage EEG, ≤ 20 µV, n=355
24-72 hrs
28 0 0-6 Low
Alpha coma --
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac arrest: A neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 1: Patients not treated with systematic review and meta-analysis. Part 1: Patients not treated with therapeutic hypothermia. Resuscitation 2013.therapeutic hypothermia. Resuscitation 2013.
Predictors of Poor Outcome: THPredictors of Poor Outcome: TH
Background EEGBackground EEG Burst-suppressionBurst-suppression DiscontinuityDiscontinuity Generalized voltage attenuation (< 10µV)Generalized voltage attenuation (< 10µV) Lack of reactivity Lack of reactivity
Periodic dischargesPeriodic discharges Generalized periodic discharges on attenuated Generalized periodic discharges on attenuated
backgroundbackground
Predictors of Poor Outcome: THPredictors of Poor Outcome: TH
Prospective, 111 adult survivors of cardiac arrestProspective, 111 adult survivors of cardiac arrest Unreactive EEG background strong predictor of mortality Unreactive EEG background strong predictor of mortality
and poor long-term neurologic recovery (FP = 7%)and poor long-term neurologic recovery (FP = 7%) Motor response to pain (FP = 24%)Motor response to pain (FP = 24%) 2+ risk factors = specificity 1.0; PPV 1.02+ risk factors = specificity 1.0; PPV 1.0
Bilaterally absent cortical SSEPBilaterally absent cortical SSEP Unreactive EEGUnreactive EEG Early myoclonusEarly myoclonus Incomplete recovery of brainstem reflexesIncomplete recovery of brainstem reflexes
Rossetti AO et al. Ann Neurol 2010;67:301-307Rossetti AO et al. Ann Neurol 2010;67:301-307
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: THCardiac Arrest: TH
Meta-analysis of 37 studiesMeta-analysis of 37 studies 2403 adult patients, comatose after cardiac arrest2403 adult patients, comatose after cardiac arrest Outcomes assessed by Cerebral Performance Category Outcomes assessed by Cerebral Performance Category
(CPC)(CPC) CPC 4-5 vs. 1-3CPC 4-5 vs. 1-3 CPC 3-5 vs. 1-2CPC 3-5 vs. 1-2 Variable timing: hospital discharge to 12 mosVariable timing: hospital discharge to 12 mos
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 2: Patients arrest: A systematic review and meta-analysis. Part 2: Patients treated with therapeutic hypothermia. Resuscitation 2013.treated with therapeutic hypothermia. Resuscitation 2013.
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: THCardiac Arrest: TH
Finding Timing Sensitivity FPR 95% CI
Quality
Bilateral absent SSEP
During TH
28 0 0-2 Moderate
Bilateral absent SSEP
After TH 42 0 0-4 Low
Absent pupillary + absent corneal + motor response ≤ extension, n = 103
72 hrs 15 0 0-8 Very low
NSE, S-100B Variable -- -- Very low
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 2: Patients arrest: A systematic review and meta-analysis. Part 2: Patients treated with therapeutic hypothermia. Resuscitation 2013.treated with therapeutic hypothermia. Resuscitation 2013.
Predictors of Outcome after Predictors of Outcome after Cardiac Arrest: THCardiac Arrest: TH
EEG Finding Timing Sensitivity FPR 95% CI
Quality
Burst-suppression During TH
37 0 0-5 Low
Burst-suppression After TH 18 0 0-5 Low
Status epilepticus from burst-suppression
Any time 42 0 0-5 Low
Nonreactive background
After TH 62 0 0-3 Low
Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor Sandroni C, Cavallaro F, Callaway CW, et al. Predictors of poor neurological outcome in adult comatose survivors of cardiac neurological outcome in adult comatose survivors of cardiac arrest: A systematic review and meta-analysis. Part 2: Patients arrest: A systematic review and meta-analysis. Part 2: Patients treated with therapeutic hypothermia. Resuscitation 2013.treated with therapeutic hypothermia. Resuscitation 2013.
ConfoundersConfounders
Sedating medicationsSedating medications Propofol, midazolam, pentobarbitalPropofol, midazolam, pentobarbital
Presence of multiple etiologies (e.g. post-arrest + hepatic Presence of multiple etiologies (e.g. post-arrest + hepatic or renal failure)or renal failure)
ArtifactArtifact Shivering / EMGShivering / EMG Electrode artifactElectrode artifact
ConclusionConclusion Use EEG for patients with altered mental statusUse EEG for patients with altered mental status
Objective measure for encephalopathyObjective measure for encephalopathy Narrow differential diagnosis when etiology unknownNarrow differential diagnosis when etiology unknown
Serial or continuous studies may be helpfulSerial or continuous studies may be helpful EEG can help with prognostication when etiology is knownEEG can help with prognostication when etiology is known
Better at predicting poor outcomeBetter at predicting poor outcome Early inaccurate prognostication may result in self-fulfilling Early inaccurate prognostication may result in self-fulfilling
prophecy: early withdrawal of careprophecy: early withdrawal of care Large prospective studies needed to determine prognostic Large prospective studies needed to determine prognostic
value of CEEG across multiple etiologies and severity of value of CEEG across multiple etiologies and severity of illnessillness