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

References and Links

LITFL

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]

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

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

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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