Electroencephalogram (EEG)

OVERVIEW

  • Electroencephalography (EEG) is the recording of electrical activity along the scalp, which corresponds to the voltage fluctuations caused by  ionic current flows within brain neurons.
  • EEG seizure patterns are highly variable, however ictal discharges are typically rhythmic and demonstrate evolution in frequency and spatial distribution over the course of the seizure

USES

  • coma
  • distinguishing epileptiform seizure activity from non- epileptiform activity (e.g. myoclonus, psychogenic presentations)
  • adjunct to brain death determination
  • prognostication (e.g. hypoxic brain injury, intracranial haemorrhage, TBI)
  • encephalopathy (e.g. hepatic, metabolic)
  • depth of sedation
  • response to treatment (e.g. anti-epileptic drugs)

METHOD OF USE

  • Recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells.
  • Some systems use caps or nets into which electrodes are embedded (e.g. high density arrays)
  • Electrode locations specified by the International 10-20 system
  • The representation of the EEG channels is referred to as a montage
  • Concurrent video monitoring may be performed

EEG PATTERNS

Posterior alpha (8-13 Hz) background activity, attenuated by eye-opening

Normal awake adult

  • Psychogenic seizures (pseudoseizures)
  • Psychogenic coma (pseudocoma)

Coma patterns:
non-reactive (monotonous) diffuse activity (several types: e.g., alpha coma, beta coma, theta coma)
burst-suppression pattern (flat-line tracing interrupted by bursts of sharply contoured activity)

Poor prognosis for meaningful neurological recovery (in absence of reversible factors)
Assess clinical and EEG reactivity to auditory, tactile, photic

  • Drugs
  • Hypoxic-ischemic encephalopathy

Electrocerebral inactivity/silence (ECI/ECS): flat-line tracing

Absence of synchronized neuronal activity

  • Drugs
  • Hypothermia
  • Brain death

Generalized slowing: theta (4-7 Hz) and/or delta (<4 Hz)

Diffuse cerebral dysfunction

  • Diffuse encephalopathy

Focal slowing: theta or delta frequency

Focal cerebral dysfunction

  • Tumor
  • Stroke

Asymmetry: lateralized difference in amplitude of background activity

Increase: skull defect
Decrease: focal injury or extra-axial collection

  • Post craniotomy
  • Subdural haematoma

Triphasic waves, occurring periodically

Diffuse encephalopathy, usually metabolic

  • Hepatic encephalopathy
  • Uraemic encephalopathy

Periodic lateralized epileptiform discharges (PLEDs): sharp-wave-slow-wave complexes occurring periodically

Acute focal cerebral injury

  • Stroke
  • Herpes simplex encephalitis

CCC Neurocritical Care Series

Journal articles

  • Bennett C, Voss LJ, Barnard JP, Sleigh JW. Practical use of the raw electroencephalogram waveform during general anesthesia: the art and science.Anesth Analg. 2009 Aug;109(2):539-50. doi: 10.1213/ane.0b013e3181a9fc38. Review. PubMed PMID: 19608830. [Free Full Text]
  • Rampil IJ. A primer for EEG signal processing in anesthesia. Anesthesiology. 1998 Oct;89(4):980-1002. Review. PubMed PMID: 9778016. [Free Full Text]

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the  Clinician Educator Incubator programme, and a CICM First Part Examiner.

He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.

His one great achievement is being the father of three amazing children.

On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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