The 'Nuts & Bolts' of Successful Long Term EEG Recording
The ‘Nuts & Bolts’ of Successful Long Term EEG Recording
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!
- Electrodes –
Cups - 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.
Two standard sizes of cups are available –
- 6mm – Usually used on premature infants and heads with circumference smaller than 40cm.
- 10mm gold cup electrode – Usually adults and heads with circumference greater than 40cm.
- Self stick pre-wired –Contain a silver/silver chloride gel.
- Skin prep - Abrasive prep used to lower impedance of the electrode connection by cleaning the area where the electrode will be applied from oils, dried skin and slightly abrades the skin. There are several brands available, such as Nuprep, Lemon Prep, Skin Pure, etc.
- Conductive paste – Serves as a media to adhere electrodes to the scalp and to ensure lowering of the contact impedance at the electrode-skin interface. Examples include Ten20 and Elefix. EC2 Electrode Cream is also a conductive paste, but for long term monitoring, we use it more for its adhesive properties rather than its conductive properties.
- Cotton tip applicators – to apply the skin prep.
- Cling gauze – to wrap the head after electrodes are secure.
- Grease pencil / china marker – to mark the head during electrode measuring.
- Tape measure (cloth or paper) – to measure the head.
- Gauze squares or cotton balls – may be used to cover the individual electrodes and help them stay in place.
- Tape – Silk, plastic or Hepafix tape. Hepafix tends to hold tight and is usually the tape of choice when securing electrodes to the skin. Silk tape also works well. Paper tape should be avoided for long term exams.
- Measure the head according to the international 10/20 system of electrode placement and mark the electrode placement locations with an ‘X’ using a grease pencil /china marker. Refer to online literature or other publications for specifics instructions for measuring the head as per the International 10/20 system of electrode placement.
- Apply electrodes to the scalp as per the 10/20 system.
- Prep the marked locations with the skin prep – Using a cotton tipped applicator, apply a small amount of prep to the center of the X, wipe several times in one direction over that spot. Wiping in one direction wipes away dead skin cells and oils and is gentle on the skin. Continue to prep all the locations that were marked.
- Apply the electrodes to the scalp – Fill the cup till 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 or piece of cotton (cut a gauze pad into 1”x1” squares cover the attached electrode). Frontal electrodes or any electrodes placed on an area that does not have hair can be secured with silk or Hepafix medical tape.
Tip –Ten20 or Elefix paste tend to not dry out as fast as other pastes. Place Ten20/Elefix in the electrode cup, follow by placing EC2 paste over the electrode. This will help the electrode stay secure. EC2 dries hard, to hold the electrode in place while the Ten20/Elefix paste remains pliable and conductive for longer recordings.
- Plug the electrodes into the Trackit. Plug the touchproof end of the electrode into the Trackit using the appropriate inputs for your labs setup.
- Wrap the head with Cling Gauze or use a stocking cap. Start by wrapping around the circumference, then crisscross over the top, then wrap around again securing the ones that were crisscrossed over the top. Insure 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.
- Pigtail the electodes – Secure the electrode wires together. Bundling the wires allows the common mode rejection to be effective in eliminating artifact from the recording.
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