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
CCC Neurocritical Care Series
Emergencies: Brain Herniation, Eclampsia, Elevated ICP, Status Epilepticus, Status Epilepticus in Paeds
DDx: Acute Non-Traumatic Weakness, Bulbar Dysfunction, Coma, Coma-like Syndromes, Delayed Awakening, Hearing Loss in ICU, ICU acquired Weakness, Post-Op Confusion, Pseudocoma, Pupillary Abnormalities
Neurology: Anti-NMDA Encephalitis, Basilar Artery Occlusion, Central Diabetes Insipidus, Cerebral Oedema, Cerebral Venous Sinus Thrombosis, Cervical (Carotid / Vertebral) Artery Dissections, Delirium, GBS vs CIP, GBS vs MG vs MND, Guillain-Barre Syndrome, Horner’s Syndrome, Hypoxic Brain Injury, Intracerebral Haemorrhage (ICH), Myasthenia Gravis, Non-convulsive Status Epilepticus, Post-Hypoxic Myoclonus, PRES, Stroke Thrombolysis, Transverse Myelitis, Watershed Infarcts, Wernicke’s Encephalopathy
Neurosurgery: Cerebral Salt Wasting, Decompressive Craniectomy, Decompressive Craniectomy for Malignant MCA Syndrome, Intracerebral Haemorrhage (ICH)
— SCI: Anatomy and Syndromes, Acute Traumatic Spinal Cord Injury, C-Spine Assessment, C-Spine Fractures, Spinal Cord Infarction, Syndomes,
— SAH: Acute management, Coiling vs Clipping, Complications, Grading Systems, Literature Summaries, ICU Management, Monitoring, Overview, Prognostication, Vasospasm
— TBI: Assessment, Base of skull fracture, Brain Impact Apnoea, Cerebral Perfusion Pressure (CPP), DI in TBI, Elevated ICP, Limitations of CT, Lund Concept, Management, Moderate Head Injury, Monitoring, Overview, Paediatric TBI, Polyuria incl. CSW, Prognosis, Seizures, Temperature
ID in NeuroCrit. Care: Aseptic Meningitis, Bacterial Meningitis, Botulism, Cryptococcosis, Encephalitis, HSV Encephalitis, Meningococcaemia, Spinal Epidural Abscess
Equipment/Investigations: BIS Monitoring, Codman ICP Monitor, Continuous EEG, CSF Analysis, CT Head, CT Head Interpretation, EEG, Extradural ICP Monitors, External Ventricular Drain (EVD), Evoked Potentials, Jugular Bulb Oxygen Saturation, MRI Head, MRI and the Critically Ill, Train of Four (TOF), Transcranial Doppler
Pharmacology: Desmopressin, Hypertonic Saline, Levetiracetam (Keppra), Mannitol, Midazolam, Sedation in ICU, Thiopentone
MISC: Brainstem Rules of 4, Cognitive Impairment in Critically Ill, Eye Movements in Coma, Examination of the Unconscious Patient, Glasgow Coma Scale (GCS), Hiccoughs, Myopathy vs Neuropathy, Neurology Literature Summaries, NSx Literature Summaries, Occulocephalic and occulovestibular reflexes, Prognosis after Cardiac Arrest, SIADH vs Cerebral Salt Wasting, Sleep in ICU
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.
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