One of the more challenging procedures that technologists perform are the very youngest of our patients.
Having a good understanding of this level of care is essential.
The EEG changes quickly during these early stages.
Knowing the timeframe of changes is critical because what is normal one week for a neonate may be abnormal by the next week.
The normal neonatal EEG exhibits many characteristics that would be considered abnormal in an adult:
diffuse slowing
discontinuity
asynchrony
and minimal reactivity
But all of these unique characteristics should evolve, in normalized increments over time, into the familiar tracings of infants.
What characterizes a Neonate?
The ACNS guideline states: Postmenstrual age less than 48 weeks.
2 months or younger for a full term infant
What characterizes full term?
Gestational Age: 38 - 40 weeks
Gestational age = the length of the pregnancy
Chronological age = the time since the baby’s birth
Post Menstrual Age (PMA) = Gestational Age + Chronological Age
Gestational age matters.
Sleep is also very different in a neonate.
The background of a neonatal EEG is broken down into awake, quiet sleep, and active sleep states.
Awake is marked simply by the presence of the eyes being open, and asleep by the eyes being closed.
Active sleep is similar to REM in adults, and is marked by the eyes being closed but with other activity such as eye movements, irregular respirations / apnea episodes, and sometimes body movements.
Quiet sleep is characterized by the eyes being closed with minimal eye movements and regular respirations. Generally, neonates move from awake into active sleep, then into quiet sleep (they spend about 50/50 in each type of sleep).
However, for up to 29 weeks of postmenstrual age the neonatal EEG looks essentially the same across the awake, active sleep and quiet sleep states.
Some Key Points When Monitoring a Neonate
Electrodes should be placed according to the International 10-20 system, modified for neonates. A full array of electrodes may be placed, according to the International 10-20 system, but this is not mandatory.
In addition to scalp electrodes, extra cerebral channels including electro- cardiogram and respiratory channels, should be used. Eye leads (for electrooculogram) and surface electromyography leads are often useful but are not universally required.
The EEG background assessment requires a minimum of 1 hour of recording time to allow analysis of sleep– wake cycling, if present.
It is recommended that neonates at high risk for seizures be monitored with conventional EEG for 24 hours to screen for seizures. (High risk often are those that have had an HIE at birth)
Another feature of the Neonatal EEG includes Discontinuity
As long as the periods of flat activity— Interburst Intervals (IBI)—remain within expected durations for their age, it is normal.
The acceptable IBI shortens over time
up to 60 seconds at 24 weeks PMA
40 seconds at 26 weeks
20 seconds at 28 weeks
10 seconds from 34-36 weeks
and 6 seconds from 37-40 weeks
After 40 weeks, you can still see some discontinuity in sleep but by 46 weeks at the most, the tracing should be completely continuous during both sleep and awake states.
IBI decreases across development - Synchrony and Reactivity increase
Trace Discontinu:
From 30-32 weeks PMA, quiet sleep is predominated by a trace discontinu pattern, marked by bursts with interburst intervals, lasting 15 seconds or less.
Trace Alternans:
Starting at 34 weeks PMA, trace discontinu evolves into trace alternans, in which interburst intervals are higher amplitude -- 25 microvolts or above -- and the IBI continues to shorten.
From 38 weeks PMA onward trace alternans continues to evolve into slow wave sleep.
Some other Neonatal EEG terms to be familiar with:
• Delta brushes - (seen only in mildly premature newborns) 8-20 Hz fast activity overriding delta waves, like the bristles on a brush. It arises around 28 weeks rather diffusely, should become mostly posterior by 36 weeks, and usually goes away completely by 40 or, at most, 42 weeks.
• Encoches Frontales - Starting around 34 weeks PMA, frontal sharp transients, or encoches frontales, arise. These are bifrontal and synchronous frontal discharges that are normal from 34 weeks to up to 46 weeks. Note that they should always be synchronous, as lack of synchronicity for them suggests it to instead be an abnormal epileptiform discharge.
As always the best source for information comes from the ACNS Guidelines
Click Here to access the Guideline on Continuous Electroencephalography Monitoring in Neonates
Because seizures in acutely ill newborns can be common - the largest role of EEG monitoring is the surveillance for and prompt treatment of electrographic seizures.
Clinical signs such as abrupt, repetitive, or abnormal appearing movements, atypical behaviors or unprovoked episodes may be the outward clinical expression of neonatal seizures.
In many high-risk populations, neonatal seizures are common, but most are subclinical (i.e., they have no outwardly visible clinical signs and may only be identified by EEG monitoring)
Often neonatal seizures are clinically silent and the EEG is the only way you'll know they're having them.
Generally, focal or multifocal seizures are much more common than generalized seizures in neonates.
Their rhythmicity should still be apparent.
In Summary:
The neonatal EEG follows a rapidly evolving time course that reflects the maturation of the baby's brain.
Babies should be nearly fully synchronous and reactive by 32 weeks PMA
Discontinuity is common, particularly in very early stages of neonatal studies, but by 40 weeks PMA discontinuity should be limited to quiet sleep with only very short (<6 seconds) periods of attenuation
Neonates have three states of consciousness: awake, active sleep and quiet sleep
Awake and active sleep look similar, with mostly theta and delta frequencies that should be continuous by 40 weeks PMA; the main difference is that the eyes are closed in active sleep and open when awake
Quiet sleep is marked by trace discontinu (attenuated periods <25μV) from 30-34 weeks PMA and by trace alternans (attenuated periods >25μV) from 34 weeks to term, after which it starts to evolve to slow wave sleep.
Occipital delta / sawtooth temporal theta are seen in very premature infants, and subside by 34 weeks PMA
Encoches frontales (up to 46 weeks), delta brush (gone by 42 weeks)
Discharges that are extremely frequent, persistently in one area, or become rhythmic are concerning for epileptiform activity rather than just sharp transients
In neonates, occipital and midline sharps are more likely to be abnormal than frontal or centotemporal sharps
Neonatal seizures evolve just like adult seizures do, but are usually focal rather than generalized
Even though this population of patient's can be challenging the procedure can be very valuable to the diagnosis and treatment.
Roya Tompkins, MS, REEG/EP T, RPSGT
Resources:
Photo credit: LearningEEG.com
American Clinical Neurophysiology Society
The Neonatal EEG