How is continuity identified in the visual analysis of neonatal electroencephalogram (EEG)?

Updated: Nov 08, 2018
  • Author: Samuel Koszer, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Continuity: One of the most striking features of the neonatal EEG is its discontinuity (ie, periods of higher voltage activities followed by periods of lower ones that occur during portions of the recording). Degrees and morphologies of discontinuity vary significantly in healthy neonates according to their postconceptional age (most dramatic in young PT and almost nonexistent in healthy FT infants reaching 3-4 weeks of postnatal life). These features also vary according to the newborn's states.

  • No absolute criteria currently exist that can be used to determine whether records are excessively discontinuous. However, recent studies do provide some guidance. Hahn et al studied interburst intervals (IBIs). Conservatively stated, the maximum IBI duration should be less than 40 seconds in infants younger than 30 weeks' postconceptional age; by term, the IBIs should be less than 6 seconds in duration.

  • The most obvious abnormality of continuity is burst-suppression (BS). This pattern consists of bursts of high-voltage activity lasting 1-10 seconds. BS is composed of various features (eg, spikes, sharp waves, theta, delta), which are followed by periods of marked background attenuation (voltage < 5 µV). The bursts (highly synchronous between hemispheres) contain no age-appropriate activity. In the most austere form, this pattern is invariant, minimally altered by stimuli, and persistent throughout awake and sleep states. This pattern is easy to differentiate from the discontinuous features normally seen during NREM sleep in infants older than 34-36 weeks' postconceptional age when TA begins to emerge clearly. See the image below.

    Burst suppression. An infant of 42 weeks' postconc Burst suppression. An infant of 42 weeks' postconceptional age with asphyxia. An alternating pattern of high-voltage mixed frequency activity and voltage attenuation in a term infant indicates severe diffuse cerebral dysfunction. Compare this to tracé discontinue (TD), in which similar activity may be considered normal prior to 30 weeks' gestational age.
  • The discontinuous EEG pattern of TA is distinguished from BS by the presence of higher amplitude interburst activity, reactiveness to stimulation, and containment of EEG features normal for postconceptional age (ie, delta brushes, temporal theta, or frontal sharp transients). Most importantly, cycling of the discontinuous pattern of TA with the continuous pattern of REM sleep is prevalent.

  • Problems may arise in young PT infants (34 weeks' postconceptional age and younger) owing to discontinuous periods of practically absent activities between bursts, which are typical at this age. [5] Unlike the normal discontinuous pattern of TD, BS usually is invariant and not associated with other features characteristic of the EEGs of neonates of various postconceptional ages. Testing for reactivity, usually but not invariably absent in BS, is also helpful. In young PT infants, serial recordings are advisable before reaching the dire prognosis generally attached to BS. However, the most reliable clue to distinguish the pathological pattern of BS from the ontogenetically normal TD is an accurate postconceptional age of the infant.


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