Leah Hanson, R.EEG/EP T.
Electrodes do not have a rating system, so it is up to the sleep lab to determine which type is best for its business and patients. But how can a lab know which electrode option is most suitable? Leah Hanson, R.EEG/EP T., featured expert on Sleep Review ’s Expert Insight section and director of sales at Rhythmlink International LLC, answers reader questions about disposable versus reusable leads and how to compare electrodes.
Q: We run a pediatric sleep lab and our leads can take quite a beating. What drawbacks are there to the disposable leads versus reusable? Also, what is the difference between using “cup” leads and flat leads? I asked two vendors at a recent conference and they could not tell me.
Hanson: Reusable EEG electrodes and disposable EEG electrodes are more alike than they are different. Both electrode types typically use the same type of lead wire and connectors. The only difference is the “cup” itself.
A reusable EEG cup is a reliable and accepted product for quality testing. As disposables are still proving themselves against reusables with regard to their quality of recording, I would recommend doing a head-to-head comparison of reusable electrodes versus disposable electrodes on the same patient. For example, use reusables on the right and disposables on the left and compare directly. This is the most reliable way to compare quality of each lead type for your individual patient demographic and application style.
Now, the advantages of reusables are that they typically are made of 99.9% silver and coated with either silver/silver chloride or plated with gold. Because such a robust metal is used, the reusable EEG electrode can last months—a definite benefit. My experience is reusable EEG electrodes last an average of 5 months, with some longer and some shorter. An additional benefit of long product life is cost savings in certain situations. Still, the ability to reuse an electrode can be a negative as well—there is no guarantee how long it will last. It can break 30 days after first use and, depending on the warranty, this can be costly.
It should be remembered that the reusable electrode requires strict compliance with cleaning and disinfecting protocols to ensure it is safe for repeat use across multiple patients. If the skin of the patient is abraded—meaning a Q-Tip with Nuprep or any other prep is used to lightly abrade the skin—that electrode falls under the criteria of a semicritical item and requires specific disinfecting protocols. Most commercially available disinfecting solutions such as Cidex meet these criteria. Full compliance with disinfecting protocols can translate into higher labor costs to clean and disinfect a reusable electrode—a factor to consider in any cost comparison between reusables and disposables.
Still, while disposable cups may not have the same advantages as reusables, they do offer their own benefits. Disposables are designed to record as well as reusables. Typically, the cup of the disposable lead is made of a plastic that is coated with a silver/silver chloride. (This can be a negative for sleep labs that exclusively use gold.) While disposable cups are not as durable as reusable cups, they do not need to be because of their single-use design. In addition, they offer the best risk management option due to the elimination of cross contamination because they are not reused.
While the direct cost of disposables will show an immediate savings on a single unit basis compared to the reusable product, there are additional costs associated with handling increased inventory, which should be considered.
Ultimately, a sleep lab needs to weigh the pros and cons of both. Some labs may find it efficient and cost-effective to use a combination of both reusables and disposables.
As for the second part of your question about cup design versus flat electrode design, the cup itself is designed to hold the conductive paste, essentially acting as a storage space. The problem with the cup design is that the patient’s body heat can cause the paste to melt or dissipate as soon as the lead is placed on the patient. As a result, the surface area of the cup no longer has consistent contact with the conductive material, potentially leading to pops and other artifact issues as the testing proceeds. A good covering, however, can be placed over the cup to keep the paste in place longer.
Flat electrodes—whether disposable self-adhesive stickies or reusable flat electrodes—can better retain the consistency of the conductive material in contact with the electrode. Thus, the flat lead should allow for more consistent recording quality for longer periods of time. Additionally, while flat electrodes can take time to get used to and may require slight adjustments in application techniques, they can be more comfortable for the patient and have been shown to cause less skin irritation than some cup designs. This may be of importance with pediatric patients for whom comfort and skin irritation can be an issue.
But, again, each sleep lab should compare the two options in their own facility to decide which type is best.
Q: 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.
Hanson: Gels and sprays make the impedance challenge much harder to conquer. Keep educating the patients, and in the meantime simply keep using a bit more elbow grease to adequately prep the area. Since you are aware of the extra challenges gels and sprays in the hair pose, be sure all 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 that its features can work properly and produce clean-looking, high-quality data. So, if you cannot get to 5K because of difficult patient scalps, can you get to 10K, 12K, or 15K consistently? If so, make your policy for all leads to be within 10 to 15K. This will ensure that your amplifier collects “common” noise between electrodes, and that it better uses its common mode rejection (CMR) feature 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 because impedances are not balanced. Even if your impedances are higher but balanced, the amplifier can eliminate “common” noise using its CMR feature.
Long story short, we cannot control patients, but we can control our impedances and the maximum assistance of our amplifiers.
Q: How are similar electrodes rated? Is one “better” than another (more stable, for instance)?
Hanson: Currently, electrodes do not have a rating system. The decision of which electrode to use depends on budget, patient demographics, and, frequently, personal preference.
If you compare electrodes, there are a few differences, such as metal types, including gold, silver or silver/chloride, tin, platinum, etc. Now these metal types are often just on the outside of the electrodes—for example, a gold cup is typically an electrode made with a silver base with a gold plating on top. The purpose of the metal is to conduct, and each lab may decide which metal produces the best data for their service. Gold is usually preferred for polysomnography (PSG) because it has been shown to enhance the slower frequencies—a feature that is important for PSG labs. EEG and epilepsy labs tend to prefer silver metals because they accentuate the faster frequencies. I will admit that I have used many different types of metals, and I have difficulty telling the difference in data results.
Beyond the metal, there are differences in how the cup shape is made. A stamped-style electrode typically has a bigger cup capacity and a thinner thickness versus the casted style, which has a thicker metal cup with a smaller cup capacity in some cases. Both collect data equally well. Additionally, some casted styles have a thinner rim that touches the patient than stamped-style electrodes. As a result, some labs prefer a casted style for skin integrity issues.
Another difference between electrode styles is how the lead wires are made. Some are made of copper, or tinsel, or another material. This is what makes different lead wires “feel” different between manufacturers. The differences in construction are a result of cost and artifact management.
Each type of lead can support data collection. Ultimately, the choice of which type to use is up to each lab. To compare different types, I recommend calling manufacturers and asking for samples for comparison purposes. Then, do your own head-to-head comparison. Remember, you can use different leads from different manufacturers; however, I would avoid mixing metals on the same patient or using different types of conductive paste. But the same metal type with the same paste or gel should produce a solid comparison.