The 'Nuts & Bolts' of Successful Long Term EEG Recording
Long Term EEG Recording Techniques from the Professionals
What do you do before you begin recording and monitoring? With a myriad of EEG products and application methods to choose from, how do you make the best possible choices for you and your patient?
In this month’s Tech Tip you’ll see the necessary supplies and best practice application techniques to help you achieve a successful EEG study every time - as recommended by EEG technologists.
Don't Leave Home Without These
Cups - Electrode cups are available in several different metals. Silver/silver chloride or gold cup electrodes are recommended due to their superior recording properties. When the skin is prepped appropriately they allow for a low impedance. Whether they’re disposable or reusable, the important thing is to capture EEG data from areas of the brain over a long period of time.
There are two standard sizes of cups are available:
- 6mm - Usually used on premature infants and heads with a circumference smaller than 40cm.
- 10mm gold cup electrode – Usually adults and heads with a circumference greater than 40cm
- So what electrode length is best?
- 48-inch electrodes are recommended for routine EEG less than two hours
- 60-inch electrodes are recommended for long term monitoring (LTM)
- Remember to not mix electrode lengths! Common mode rejection works best when electrodes are the same metal and length and when impedances are low and balanced.
- Skin prep - An abrasive prep used to lower the impedance of the electrode connection by cleaning the area of oils and dried skin where the electrode will be applied. The skin will be slightly abraded, so use caution if your patient has sensitivity. There are several brands available, such as Nuprep, Lemon Prep, Skin Pure, etc. There are different price points and advantages to consider, while some technologists just prefer a certain type due to familiarity.
- Conductive paste – This serves as a media to adhere electrodes to the scalp and to ensure lowering of the contact impedance at the electrode-skin interface. Typical routine pastes include Ten20 and Elefix. This paste can be used alone for routine studies because it is easy to remove. If used alone, it is not recommended to use for LTM recordings. For LTM studies, a stronger hold conductive paste/gel is suggested like Tensive, SAC2 and EC3. Collodion is also a tried and true option, although the odor is quite strong. Facilities may require air circulation when using Collodion, so using it may not always be an option.
- Cotton tip applicators – to apply the skin prep. For best results, apply in a single direction. Alcohol wipes can assist in addressing difficult impedance issues, such as oils, hair products, and patients with a very dry scalp.
- Kerlix roll and Tubular Elastic Retention Netting - these are an option for headwraps and securing electrodes.
- Cling gauze – to wrap the head after electrodes are secure. Having additional types of gauze can be useful for other applications as well. No matter if you are using Kerlix, Tubular Netting, or Cling gauze, the best practice is to use the least amount of wrap required to make sure the electrodes are secure. If it’s too thick or tight, the patient will be uncomfortable and sweat. This causes the paste to melt and break down the patient’s skin.
- Surgical markers – Used to mark the head during electrode measuring. Single-use markers like surgical markers are recommended due to regulations regarding cross-contamination.
- Tape measure (paper or cloth) – to measure the head. If your measuring tape is reusable, we recommend removing the tape from the dispenser reel so the tape can be cleaned. You don’t want particles trapped in the reel!
- Gauze squares or cotton balls – may be used to cover the individual electrodes and help them stay in place. These can be used with any of your conductive pastes/gels, and even collodion.
- Skinsavers - reduce pressure from electrodes and can help prevent skin breakdown, but may not be right for every patient. Use on a case-by-case basis.
- Tape – Silk, paper, Transpire, Coban, or Hypafix tape. Hypafix tends to hold tight and is usually the tape of choice when securing electrodes to the skin (not recommended on hair).
- Silk tape also works well. Paper tape should be avoided for long-term exams.
- Silk and Transpire tape are useful in securing headwraps, while Coban is useful for bundling electrodes.
Application Techniques & Tips - Step-by-Step
1. Measure the head according to the international 10/20 system of electrode placement and mark the electrode placement locations with an ‘X’ using a marker. Refer to online literature or other publications for specific instructions for measuring the head as per the International 10/20 system of electrode placement.
2. Apply electrodes to the scalp as per the 10/20 system.
- Prep the marked locations with the skin prep – Apply a small amount of prep to your cotton-tipped applicator, and wipe on the center of the X several times in one direction. Wiping in one direction wipes away dead skin cells and oils and is gentle on the skin. An alcohol pad may assist in lowering the impedance. Continue to prep all the locations that were marked. If you prep one spot at a time, you decrease the chance of losing your spot or skipping one and having to go back to it.
- Apply the electrodes to the scalp – Fill the cup until slightly overflowing with paste. Press the cup onto the location that was prepped using gentle downward pressure (some paste may ooze out of the sides of the cup and out of the hole in the center of the cup). Cover the electrode with a small gauze square, tape, or piece of cotton (cut a gauze pad into 1”x1” squares to cover the attached electrode). Frontal electrodes or any electrodes placed on an area that does not have hair can be secured with tape or Hypafix.
- Ten20 or Elefix paste tends to not dry out as fast as other pastes. Place Ten20/Elefix in the electrode cup, followed by placing EC3, Tensive, SAD2 paste over the electrode. This will help the electrode stay secure. EC3, Tensive, and SAD2 dries hard to hold the electrode in place while the Ten20/Elefix paste remains pliable and conductive for longer recordings.
3. Plug the electrodes into your EEG amplifier.
4. Wrap the head with Cling Gauze or use a stocking cap. Start by wrapping around the circumference, then criss-cross over the top, then wrap around again securing the ones that were crisscrossed over the top. Ensure that the wrap around the head goes under the inion, this will help to keep it from sliding up. Finally, wrap around the chin and use tape to secure any loose ends.
5. Pigtail the electrodes – Secure the electrode wires together. As we mentioned before, Coban tape is useful for bundling. Bundling the wires allows the common-mode rejection to be effective in eliminating artifacts from the recording. See more advice on how to reduce EEG artifacts here.
As technology changes, technologists have adapted their workflows, too. The days of massive computers on wheeled carts are thankfully behind us, allowing improved service to patients. If you enjoyed the information in this article, you may enjoy our article on preparing your patient for an in-home EEG recording. Join our Lifelines Neuro Insider list to receive updates about EEG tech tips or other helpful information of your choosing.