EEG-signals

Expert Advice:  Electrodes     Impedances

                             Disinfect Electrodes       Pediatric Leads

How can we overcome poor EEG signals when a patient uses an overabundance of hair gel or spray (despite our instructions)? We work hard to get great impedance values with these patients, yet still have unacceptable waveforms.

It’s a tough one. Gels and sprays make the impedance challenge much harder to accomplish. Keep educating the patients and in the meantime simply keep using a bit more “elbow grease” to adequately prep the area. And, since you know you have extra challenges due to gels and sprays in the hair, be sure all of your impedances are low and balanced. Being balanced is as important as having low impedances.

Your “best friend” for good quality data is your collection system and its ability to assist in cleaning up artifact. The equipment’s amplifier is looking for balanced electrodes so the amplifier’s features can work properly and produce clean looking high quality data. So, if you can’t get to 5K because of difficult patient scalps, can you get to 10k or 12K or 15K consistently? If so, make your policy for all leads to be within 10-15K and this will ensure your amplifier collects “common” noise between electrodes and can better use the amplifier’s common mode rejection features to eliminate the unwanted noise. It is better to have 10 electrodes showing an impedance of 13K than seven electrodes reading 2K and three electrodes reading 15K. This is because if impedances are not balanced the machine “views” the noise differently and it cannot be processed as common artifact. Even if your impedances are higher but balanced, the amplifier can eliminate “common” noise using its CMR (common mode rejection) feature of the amplifier.

Long story short, we can’t control the patients but we can control our impedances and the maximum assistance of our amplifiers. Balanced and as low as possible will ensure good clean data despite the patient’s lack of preparation.