When the Head is the Size of an Orange
EEG in the Neonatal Population, 10/20 Full Array or Modified Placement
By Melissa Burke, R.EEG/EP T., CNIM
Social media can be a great way to share information and get feedback. There are several forums for those in the EEG community, and there are active discussions on best practices. Recently on Facebook, there was an interesting discussion regarding continuous EEG (cEEG) in the NICU. The question that started the thread went something like this:
“How can you apply a full set of 10/20 electrodes on a neonate’s head, which is the size of an orange, without getting a salt-bridge?”
There was a great deal of participation in this discussion, a sure indication it struck a chord to many in the neurodiagnostic field of cEEG in the NICU population. The 10/20 full electrode placement is frequently used in the U.S. on all neonate head sizes and ages. However, a summary of the Facebook discussion follows, with many practices that allow for a modified placement of electrodes for neonates.
Many sites base the number of electrodes used for neonatal EEG monitoring on the baby’s gestational age and head circumference. The protocols varied from site to site, with some being more common and used at several sites.
- Gestational age 52 weeks or less with a head circumference of less than 33cm=double distance
- Gestational age 46 weeks or less with head circumference of 35cm or less=double distance
Some sites base the amount of electrodes on head circumference only.
- 30cm head circumference or less=double distance
- 33cm head circumference or less=double distance
- 35cm head circumference or less=double distance
- 38cm head circumference or less=double distance
Another developing practice is to eliminate the Fp1 and Fp2 frontal electrodes as these tend to be a common location for skin irritation. Instead, Fp3 and Fp4 are used. Fp3 is located halfway between the conventional electrode locations FP1 and F3. Fp4 is located halfway between the conventional electrode locations of FP2 and F4.
A common practice is to eliminate F3, F4, P3, and P4 from the standard 10/20 placement. These are the most common double distance electrodes used:
- Fp1, T3, 01, C3
- Fp2, T4, 02, C4
- Fz, Cz, Pz
- T3 -01
A variation of the above electrode placement eliminates Fp1 and FP2, replacing with FP3 and FP4:
- FP3, T3, 01, C3
- FP4, T4, 02, C4
- Fz, Cz, Pz
- T3 -01
Advances in single disposable electrode arrays such as the Incereb neon8 and neon12 are also being used for NICU monitoring. These can be easily applied by nurses, technologists, or hospital staff. They are pre-measured for symmetrical placement, pre-filled with Ten/20 Conductive Paste®, and come supplied with Nu Prep® Skin Prep to gently rub under each electrode site. After prepping the scalp, residual Nu Prep should be wiped from the baby’s scalp.
The neon8 has six recording electrodes, along with ground and reference electrodes, and is recommended for head circumference of 31cm or less. Some of the suggested montages used by NICU bedside staff have a limited amount channels. These monitors usually use aEEG trending.
- F3, C3, P3
- F4, C4, P4
- Ground and Reference
neon8 Sample Montages
The neon12 has ten recording electrodes, along with ground and reference electrodes, and is recommended for head circumference of 32cm and above.
- F3, T3, T5, 01, C3
- F4, T4, T6, 02, C4
- Ground and Reference
neon12 Sample Montage
The most commonly used among nearly all the sites were the extra-cerebral monitoring electrodes.
- Two chin EMG leads
- Left and right eye leads with variable placements
- 1-2 EKG leads
- Respiration bands
Methods of electrode application varied from collodion to paste secured with paper tape, or self–adhesive gauze, for cup or webbed electrodes. For application of the neon8 and neon12, a light head wrap or cap will hold the electrodes in place.
NICUs across the country are also using amplitude integrated EEG trends (aEEG). This practice is especially popular with the nurses in the neuro-NICU environment, as well as with technologists, neonatologists, and neurologists. Some sites use the aEEG trend in a two or three channel display, and the nurses apply electrodes. More and more frequently, nurses are recognizing aEEG at the bedside is an important tool to access and monitor the neonatal brain, and they are becoming more comfortable doing it.
The aEEG trends are used during cEEG monitoring along with raw EEG signals and other trends shown in the picture below. Following this is an educational overview of best practices for neonatal monitoring, courtesy of the Lifelines iEEG Trends Guide (2018).
Amplitude integrated EEG (aEEG)
The aEEG displays minimum and maximum amplitude of all background activities over a preset time interval. It provides a good measure of background activity and is sensitive for recognition of burst- suppression activity and seizures. The aEEG trend has been used for decades in the neonatal field for seizure detection and evaluation of background activity, which affects prognosis of the critically ill child.
The aEEG gives a compressed view of the variation in amplitude of the EEG. The signal is typically recorded, amplified, filtered and processed. The EEG processing includes semi-logarithmic amplitude scaling, rectifying, smoothing and time compression. The trend is traditionally displayed at the speed of 6 cm/hour. This is however changing and experts are getting more and more comfortable in using the trend with a different time scale.
Below is a screenshot of the aEEG trend for each side of the brain (F4- C4 and F3-C3) and a transverse channel (C4-C3). Below the aEEG trend is a Burst Suppression (BS) trend (see later) and the raw EEG data, which is necessary to verify the information in the aEEG trend.
As explained in the NICU chapter of this document the aEEG trend has been used successfully by neonatologists for decades to monitor the newborn brain. Previous and recent studies support the use of the trend bedside in the NICU and experts have expressed the trend to be a reliable monitoring tool, especially when raw EEG data is accessible to support the interpretation.
Using the aEEG Trend in the NICU, allows non EEG experts to visually identify changes that may reflect abnormal brain function and seizure activity that have no or very little clinical manifestation. With iEEG, the clinical staff can consult an EEG expert for further interpretation. The expert is then able to: verify what is happening in the trend by looking at the raw EEG data online; conduct treatment; and monitor the treatment.
The information gathered shows here are many options for monitoring the brains of neonates. While there is no single best practice, there are alternatives to the full 10/20 electrode array for neonates. The overarching goal is to monitor the brains to improve outcomes.
Please refer to the American Clinical Neurophysiology Society Guidelines on Continuous EEG monitoring in Neonates while developing your NICU protocols.