EEG in Critical Care

Indications for EEG

Terminology

International 10-20 system

5x transverse planes, 5x sagittal places. Odd numbers on the left, even numbers on the right, "z" = midline. Fp = frontopolar, F = frontal, C = central, T = temporal, P = parietal, and O = occipital. A "montage" is a specific configuration of electrodes to aid localization.

Characterizing EEGs

Rhythms

  1. Alpha rhythm (posterior dominant rhythm) is a symmetrical 8-12 Hz pattern best seen in the posterior scalp. Increased in amplitude during wakefulness and is more reactive if the patient is alert.
  2. Theta waves are moderately slow rhythms (4-7 Hz) associated with encephalopathy:
  3. Delta waves are markedly slow rhythms (<4 Hz) associated with encephalopathy.
    1. Polymorphic delta activity (PDA) indicates asymmetric/polymorphic delta waves. Example:

Reactivity

Patterns of EEG

"Normal" EEG

Relative to each individual patient's baseline; however the typical normal EEG is characterized by an alpha rhythm with preserved reactivity. Most patients in the ICU will NOT have this due to critical illness.

Slowing

Slowing of the normal alpha rhythm suggests encephalopathy. As the encephalopathy worsens, the EEG becomes increasingly slow (alpha --> theta --> delta).

Diffuse slowing, severe slowing, or PDA occurs in a range of clinical presentations such as hepatic failure, renal failure, sepsis, drug intoxication, hypoxia, head trauma.

Focal slowing is indicative of an underlying parenchymal lesion (abscess, hematoma, tumour, ischemia, recovery form focal seizure, etc). For example, focal slowing over left temporal head region:

References

  1. EEG interpretation and ictal-interictal continuum. EMCrit Project. Accessed May 11, 2023. https://emcrit.org/ibcc/eeg/

  2. Kubota Y, Nakamoto H, Egawa S, Kawamata T. Continuous EEG monitoring in ICU. j intensive care. 2018;6(1):1-8. doi:10.1186/s40560-018-0310-z

  3. Anderson D, Jirsch JD, Wheatley MB, Brindley PG. Electroencephalogram patterns in critical care: A primer for acute care doctors. Journal of the Intensive Care Society. 2022;23(1):58-69. doi:10.1177/1751143720949454

  4. Sharma S, Nunes M, Alkhachroum A. Adult Critical Care Electroencephalography Monitoring for Seizures: A Narrative Review. Frontiers in Neurology. 2022;13. Accessed May 11, 2023. https://www.frontiersin.org/articles/10.3389/fneur.2022.951286

  5. Sewell L, Abbas A, Kane N. Introduction to interpretation of the EEG in intensive care. BJA Educ. 2019;19(3):74-82. doi:10.1016/j.bjae.2018.11.002

  6. Rubinos C, Alkhachroum A, Der-Nigoghossian C. Electroencephalogram Monitoring in Critical Care. Semin Neurol. 2020;40(6):675-680. doi:10.1055/s-0040-1719073