The Three S’s of aEEG – Sleep – Symmetry – Stability

The Three S’s of aEEG

We believe that no beside monitoring plan in the NICU should leave out the most important organ of them all…the brain!  And tools such as video-EEG and amplitude-integrated EEG (aEEG) are used worldwide to continuously monitoring neonatal brain function.

aEEG is a great solution for NICU’s looking to improve their brain monitoring program because it is easy to use and easy to read (with practice), making it a powerful tool for the bedside NICU clinician.

In this article, we go beyond the typical use of aEEG for assessing the overall brain background and seizures and dive a bit deeper into three S’s – Sleep, Symmetry, and Stability – which are discussed in more detail in Module 4 of Synapse’s Online aEEG Mastery Course.

Here’s a sneak peek of her lecture:

#1 – Sleep-Wake Cycling

Sleep is crucial for neurosensory development, learning, and memory, as well as the preservation of neuro-plasticity.  However, in the NICU, we assess the presence or absence of sleep-wake cycling to evaluate their brain maturity, organization, level of injury or progress toward recovery.

Since aEEG records brain activity over long time periods, we can use it to assess infants as they transition in and out of different behavioral states and during caregiving activities and procedures.  For babies and adults alike, sleep-wake cycling is defined as short intervals of quiet brain activity alternating with periods of restfulness creating increased brain activity.   These different stages produce different levels of brain wave amplitude which can be recorded and trended on the aEEG monitor screen.

During periods of quiet (non-REM) sleep, the aEEG pattern becomes discontinuous (with lower margins often drifting below the 5 microvolts line).  In healthy, mature brains this discontinuous pattern will alternate every 30 to 45 minutes with a more active, continuous aEEG pattern and the upper margins of the aEEG pattern will then be greater than 10 microvolts and the lower margin will be greater than 5 microvolts.


Brain pattern cyclicity emerges as young as 28 weeks gestation and becomes robust and organized around 34 weeks gestation and is then called trace alternant.  Term infants with HIE and who undergoing cooling often times have absent sleep-wake cycling initially but the recovery of cycling before rewarming has been shown to have positive predictive value for a good outcome in this population.

Sleep is listed in the core-measures of neuro-protective care, but it is often difficult to assess in our tiny patients.   Why not use aEEG to help?   Beyond using aEEG for assessing brain injury, there exists more opportunity to use aEEG to guide the timing of our interventions and interactions with babies in the NICU and to study which interventions actually help to ensure quality and uninterrupted sleep. 

#2 – Symmetry

One of the critical elements that can be assessed with aEEG is pattern symmetry.

When aEEG was first introduced into the NICU in the late-1990’s, the devices were very simple.  They consisted of three electrodes.   One recording electrode placed over the right parietal lobe, one recording electrode placed over the left parietal lobe, and one ground electrode placed on the forehead.   

This early set-up created a “single-channel” set up, and in the literature is often referred to as the bi-parietal, cross-cerebral, or P3-P4 montage.  This single-channel was great for assessing overall brain function monitoring but it did not offer any localized information.     Remember, one pair of active, recording electrodes is all it takes to create a “channel”.   

As aEEG gained popularity in the NICU the desire to monitor brain function over larger areas and to be able to compare the left and the right hemispheres of the brain.   Most aEEG monitors today offer you the ability to add on an additional two (or more) electrodes so that you can record more than one aEEG channel.   

 With the addition of one pair of electrodes over the central sulcus area of the brain, you can create a three or four-channel aEEG recording montage.   The standard aEEG set up allows you to record and assess the electrical signal of the brain from the left hemisphere (C3-P3), the right hemisphere (C4-P4), and the classic cross-cerebral channel (P3-P4).  

It is highly recommended to compare the symmetry of electrical activity from the right and left hemispheres in addition to the cross-cerebral (P3-P4) view as it may offer clues to the presence of mechanical problems or unilateral brain injury as you can see below. 

#3 –  Stability of aEEG patterns

The true power of aEEG lies in its long-term trend over days and weeks.  However, there are sometimes opportunities to see changes to the patient’s aEEG pattern in shorter periods, and changes can be seen in a few minutes or hours.

Changes to the aEEG pattern (or lack of change too) can provide us with important clues over time such as maturity of the developing brain, progress towards recovery, the presence of seizures or in some cases, clinical deterioration.

One situation where immediate and dramatic effects can be seen on the aEEG pattern is the impact of administering medications on our patient’s brain activity. One of the most striking pictures from Session 4 of the aEEG Mastery course shows the impact of giving a benzodiazepine on brain function of a sick 27-week premature infant she was monitoring. In the tracing below, you can see an abrupt change in the background pattern at precisely the time the patient received a dose of midazolam.


Wait, I want more!

If you haven’t mastered aEEG interpretation, we have good news for you!

You can purchase Synapse’s Online aEEG Mastery Course designed to take you from novice to expert in just a few short hours.  This course is available for one-time purchase with lifetime access – or – join our new monthly continuing education club and get access to the course for as long, or as short, as you need it.   

If your entire team needs help learning aEEG classroom licenses and group discounts are also available!

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