EEG ArtifactsEEG Artifacts

Sarah Schmitt, MDSarah Schmitt, MD

Nov. 2016Nov. 2016

The perfect EEGThe perfect EEG

A “perfect” EEGA “perfect” EEG: contains only signals : contains only signals from the cerebral cortexfrom the cerebral cortex

Reality: Reality: EEG contains signals from the EEG contains signals from the cerebral cortex… many other objects near cerebral cortex… many other objects near the patient that generate an electrical fieldthe patient that generate an electrical field

EEG artifactsEEG artifacts

Scalp EEGs record tiny (microvolt) signalsScalp EEGs record tiny (microvolt) signals

Electrodes detect electrical “noise” from many Electrodes detect electrical “noise” from many other sourcesother sources

Artifacts can completely obscure underlying EEGArtifacts can completely obscure underlying EEG

Artifacts can also mimic or distort normal EEG Artifacts can also mimic or distort normal EEG brain activity, leading to misinterpretationsbrain activity, leading to misinterpretations

Artifacts and Noise in the Artifacts and Noise in the ICUICU

Cardiac

Electrodes

Telephone

Eyes

Muscle

Ventilator

Catheters, external devices

MovementMovement

Why ICU EEGs have more artifacts (and Why ICU EEGs have more artifacts (and harder to detect artifacts) than regular harder to detect artifacts) than regular EEGs:EEGs:

o ElectrodesElectrodeso ElectronicsElectronicso EquipmentEquipmento Staff and patient movementStaff and patient movemento Abnormal physiologyAbnormal physiology

ICU EEGICU EEG

ICU EEGs are often prolongedICU EEGs are often prolongedo May have worse electrode integrity over timeMay have worse electrode integrity over timeo Frequent electrode replacement may Frequent electrode replacement may skin skin

breakdownbreakdown

ICU patients may have head wounds / injuries that ICU patients may have head wounds / injuries that worse electrode integrity. Ex: worse electrode integrity. Ex:o Scalp hematoma from head traumaScalp hematoma from head traumao Drainage from craniotomy siteDrainage from craniotomy site

If not using CT / MRI compatible electrodes, may If not using CT / MRI compatible electrodes, may frequent disconnection for imaging studies frequent disconnection for imaging studieso 54% of patients are imaged during cEEG54% of patients are imaged during cEEG

Electrode integrity in the ICUElectrode integrity in the ICU

Vulliemoz S, Perrig S, Pellise D, et al. J Clin Neurophysiol. 2009 Aug;26(4):236-43.

Intensive care unit (ICU) rooms are busy Intensive care unit (ICU) rooms are busy placesplaces

o High nurse-to-patient ratioHigh nurse-to-patient ratioo Hourly vital signs, neuro checksHourly vital signs, neuro checkso Large multidisciplinary ICU teamsLarge multidisciplinary ICU teamso Patients are touched on average 103x / 24hPatients are touched on average 103x / 24ho People enter and leave room frequentlyPeople enter and leave room frequently

Frequent movement, assessment can Frequent movement, assessment can movement of EEG equipment, electrodes, movement of EEG equipment, electrodes, cables, cameras cables, cameras additional artifacts additional artifacts

ICUs and personnelICUs and personnel

Meriläinen M, Kyngäs H, Ala-Kokko T. Intensive Crit Care Nurs. 2010 Oct;26(5):246-53.

Multiple electronic devices Multiple electronic devices monitor ICU monitor ICU patientspatients

o Motorized bedMotorized bedo EKG / telemetryEKG / telemetryo Blood pressure cuffBlood pressure cuffo Pulse oximeterPulse oximetero Swan-Ganz catheterSwan-Ganz cathetero PacemakersPacemakerso Left ventricular assist deviceLeft ventricular assist deviceo Extracorporeal membrane oxygenationExtracorporeal membrane oxygenation

o Incubator (in neonatal ICUs)Incubator (in neonatal ICUs)

ICU EEG: electronic factorsICU EEG: electronic factors

MOST OF THESE DEVICES CAN POTENTIALLY CREATE ARTIFACTS

o Continuous veno-venous hemofiltration devices

o Fanso Licox tissue oximetry

monitoro Intracranial pressure

monitoro Cooling / warming

blanketso Ventilatoro IV fluid machines

Many patients in the ICU are prone to abnormal Many patients in the ICU are prone to abnormal movements due to their underlying condition:movements due to their underlying condition:

o TremorTremoro ClonusClonuso RigorsRigorso Postanesthetic shiveringPostanesthetic shiveringo MyoclonusMyoclonuso Asterixis Asterixis o PosturingPosturing

One study of delirious ICU pts found that 54.9% had One study of delirious ICU pts found that 54.9% had episodic hypermotor activity!episodic hypermotor activity!

ICUs have active patientsICUs have active patients

Peterson et al., J Amer Geriatrics Society 2006

In the ICU, physiologic artifacts are often less In the ICU, physiologic artifacts are often less recognizable due to physiologic abnormalitiesrecognizable due to physiologic abnormalities

o Eye movement artifact due to nystagmusEye movement artifact due to nystagmuso EKG artifact in the setting of cardiac arrhythmiaEKG artifact in the setting of cardiac arrhythmiao Respirator artifact with tachypneaRespirator artifact with tachypnea

ICU physiologyICU physiology

Artifacts in the ICUArtifacts in the ICU

PhysiologicPhysiologic Instrument and electrode artifactsInstrument and electrode artifacts External mechanical / device relatedExternal mechanical / device related MovementMovement

Physiologic artifactsPhysiologic artifacts Eye / ocular artifactsEye / ocular artifacts

o Blink artifactBlink artifacto Eye flutterEye fluttero Eye movements / lateral Eye movements / lateral

rectus spikesrectus spikeso NystagmusNystagmuso ERGERG

EKG artifactEKG artifacto Pulse artifactPulse artifacto Ballistocardiographic artifactBallistocardiographic artifacto PVC / arrhythmia artifactPVC / arrhythmia artifacto Pacemaker artifactPacemaker artifact

EMG artifactEMG artifact SwallowingSwallowing ChewingChewing BruxismBruxism

Glossokinetic artifactGlossokinetic artifact Respiratory artifactRespiratory artifact Galvanic skin response / Galvanic skin response /

sweat artifactsweat artifact

Respiratory artifact is magnified in tachypneic ptRespiratory artifact is magnified in tachypneic pt

Fp1-F3

F3-C3

C3-P3

P3-O1

Fp2-F4

F4-C4

C4-P4

P4-O2

Fp1-F7

F7-T 3

T3-T 5

T5-O1

Fp2-F8

F8-T 4

T4-T 6

T6-O2

Fz-Cz

Cz-Pz

LUC-A1

R LC-A2

EKG

Comment100 uV

1 sec

Because many pts in the ICU do not have eye leads placed, nystagmus or abnormal eye movements can be confused for rhythmic delta activity

Nystagmus can result from medications, cerebellar or brainstem Nystagmus can result from medications, cerebellar or brainstem lesions and can resemble frontal epileptiform activitylesions and can resemble frontal epileptiform activity

EKGEKG: : o The artifact created by the electrical signals The artifact created by the electrical signals

generated by the heartgenerated by the hearto Looks like a QRS complexLooks like a QRS complexo More prominent in pts with short, thick necksMore prominent in pts with short, thick neckso More prominent in montages that use ear as More prominent in montages that use ear as

referencereferenceo Irregular cardiac rhythms & widened QRS Irregular cardiac rhythms & widened QRS

complexes can resemble epileptiform activitycomplexes can resemble epileptiform activity

Cardiac artifactsCardiac artifacts

EKG artifact with low voltage background, wide complex EKG artifact with low voltage background, wide complex irregular tachycardiairregular tachycardia

PulsePulse: : o The artifact created by placing an electrode over The artifact created by placing an electrode over

a pulsating arterya pulsating arteryo Most common in central, temporal electrodes Most common in central, temporal electrodes o Creates a rounded artifact, time-locked to the Creates a rounded artifact, time-locked to the

EKGEKGo Irregular heart rate can Irregular heart rate can arrhythmic delta arrhythmic delta

All those cardiac artifactsAll those cardiac artifacts

Pulse artifact

Ballistocardiographic artifactBallistocardiographic artifact: : o Looks like pulse artifact: rounded artifact, time-Looks like pulse artifact: rounded artifact, time-

locked to the EKGlocked to the EKGo Created by the mechanical movement of the Created by the mechanical movement of the

heart heart moving the body moving the bodyo More common in small / thin ptsMore common in small / thin pts

All those cardiac artifactsAll those cardiac artifacts

Ballistocardiographic artifactBallistocardiographic artifact

Highly variablyHighly variablyo Can be positive or negativeCan be positive or negativeo Can occur at respiratory rate or at twice the Can occur at respiratory rate or at twice the

respiratory rate (with inhalation and exhalation)respiratory rate (with inhalation and exhalation)o May appear slow and rhythmic or sharpMay appear slow and rhythmic or sharpo More common in occipital electrodes (head More common in occipital electrodes (head

midline) or temporal / parietal electrodes (head to midline) or temporal / parietal electrodes (head to the side), but can occur anywherethe side), but can occur anywhere

Ventilator artifactsVentilator artifacts

Ventilation artifactVentilation artifact

A special type of ventilator artifactA special type of ventilator artifact Electrostatically charged water in ventilator Electrostatically charged water in ventilator

tubing rapidly oscillates with each inhalation tubing rapidly oscillates with each inhalation and exhalation and exhalation o Creates frontally predominant semi-rhythmic alpha, Creates frontally predominant semi-rhythmic alpha,

theta or beta activitytheta or beta activityo Often confused with seizureOften confused with seizureo Bursts of alpha-theta get longer and longer as Bursts of alpha-theta get longer and longer as

patient accumulates more water in their tubepatient accumulates more water in their tube Correct by suctioningCorrect by suctioning Can also monitor with chin electrodeCan also monitor with chin electrode

““Water in the ventilator tube”Water in the ventilator tube”

Water in ventilator tubeWater in ventilator tube

Water in ventilator tubeWater in ventilator tube

Electrode artifactElectrode artifact 60 Hz artifact60 Hz artifact Amplifier artifactAmplifier artifact Capacitative artifactCapacitative artifact Inductive artifactInductive artifact Electrostatic artifactElectrostatic artifact Aliasing artifactAliasing artifact

Instrument and electrode artifactsInstrument and electrode artifacts

More problems with electrode artifact in More problems with electrode artifact in the ICUthe ICUo Prolonged monitoringProlonged monitoringo Scalp integrityScalp integrity

Result = electrode artifactsResult = electrode artifacts Keep electrode impedence < 10 kKeep electrode impedence < 10 kΩΩ– –

many pts require repair 2-3 x / daymany pts require repair 2-3 x / day

Electrode artifactElectrode artifact

Bad electrode: P4 artifactBad electrode: P4 artifactFp1-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-A1

R LC-A2

E KG

Comment100 uV

1 sec

Caused by detection of signals from 60 Caused by detection of signals from 60 Hz electrical appliances near patientHz electrical appliances near patient

Big problem in the ICUBig problem in the ICUo Electrode integrityElectrode integrityo Many immobile devices surrounding ptMany immobile devices surrounding pt

When possible, move devices away from When possible, move devices away from headhead

Use 60 Hz notch filterUse 60 Hz notch filter

60 Hz artifact60 Hz artifact

60 Hz before and after60 Hz before and after

This shows a sample ICU EEG recording before (left) and after (right) use of the 60 Hz notch filter

Almost any device can produce an artifact Almost any device can produce an artifact (usually 60 Hz)(usually 60 Hz)

Particularly common device artifacts:Particularly common device artifacts:o Chest percussion devicesChest percussion deviceso Continuous veno-venous hemofiltrationContinuous veno-venous hemofiltrationo Extracorporeal membrane oxygenationExtracorporeal membrane oxygenation

External devicesExternal devices

Creates 5-6 Hz rhythmic theta activityCreates 5-6 Hz rhythmic theta activity

Because it can “spread” to adjacent Because it can “spread” to adjacent electrodes if patient moves, it can appear electrodes if patient moves, it can appear to “evolve”to “evolve”

Bed percussionBed percussion

Bed percussionBed percussion

Extracorporeal membrane oxygenation (ECMO) artifact (seen here) can usually be minimized by moving the pump away from the patient’s head

Many movements can create artifacts, Many movements can create artifacts, sometimes rhythmicsometimes rhythmic

Video is imperativeVideo is imperative Patient movementsPatient movements

o MyoclonusMyoclonuso ClonusClonus

Staff movementsStaff movementso Sternal rubSternal rubo SuctioningSuctioning

MovementMovement

Spiky, nonphysiologic phase reversals, easy to confuse Spiky, nonphysiologic phase reversals, easy to confuse with epileptic spikeswith epileptic spikes

MyoclonusMyoclonus

Sternal rubSternal rub

Can look rhythmic or evolving but usually irregular with strange field: correlate with video!

SuctioningSuctioning

Creates irregular theta and delta activity, at times semi-rhythmic

The ICU is filled with sources of artifacts!The ICU is filled with sources of artifacts!

Although steps can be taken to minimize Although steps can be taken to minimize artifacts, some artifacts are inevitableartifacts, some artifacts are inevitable

Recognize the appearance of common Recognize the appearance of common artifacts, look at patient videos and artifacts, look at patient videos and document patient activities to avoid document patient activities to avoid mistakesmistakes

ConclusionsConclusions