Expert Insight - Electrodes/Sensors

Are damaged electrodes and sensors repairable? -

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Is bleach soaking still the standard? And which works better: gold or silver eletrodes? -

Bleach soaking of electrodes or use as a disinfectant is still in use but, from my experience, has decreased in the past several years. The more frequently used disinfectant strategy is the use of commercially available disinfectants marketed specifically for certain levels of disinfection. These can be found online and from various accessory suppliers. The main reason for the trend is higher accountability of individual departments to ensure the disinfectant being used is appropriate for the type of disinfectant required for the situation. Because we “prep” the patient’s skin by abrading (rubbing). a medium to high level of disinfection of the electrodes is required. The commercially available products on the market typically list, on their product label, the level of disinfectant the product is designed to achieve and thus helps each department ensure compliance. The use of bleach and other disinfectants can certainly be used but documentation of the solution is critical and I would work with your risk management team or other appropriate department within your service or facility. If unsure, check out the commercially available options.

As for gold versus silver electrodes, either type will work but some folks just have a preference. Many are shifting to single patient disposables to eliminate the disinfecting requirement and in some cases reduce overall budget expense. A recent report from a market research group, iData Research Inc, reports that nearly one-quarter of electrodes being used are disposables.

Gold is usually more expensive but some professionals feel the low frequency data displays better with the gold metal. I would compare, compare, compare. The quality of the data relates both to your electrode and your amplifier so in many cases today's high quality amplifiers reduce differences between electrode metal types regarding data quality during testing.

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I have a room I set up at the hospital in Missouri Valley, Iowa. I always have trouble with 60 Hz interference, so I always have to use a notch filter. I have unplugged the bed and all nursing diagnostic equipment which makes it better but not clear. Is there anything else I can do? -

If possible, try the following:

1. Physically move your gear and use a different outlet.

2. Talk to Biomed/Bioengineering and ask them to check the outlets. In most cases their outlets are probably functioning correctly with the proper grounding but it's definitely worth pulling them in on the issue.

3. Talk to your equipment manufacturer as your gear could be the problem. Cables and connectors are common problems as equipment ages.

4. Is this system portable? Can you move it to see if the poor quality remains in different environments? If so, it points to your equipment or cables.

5. Do you have a second system that you can you swap out cables, amplifiers, or other peripheral gear to try to pinpoint the problem?

6. Make sure your impedances are very balanced and as low as possible. For example, if you can get all of the electrode impedances below 10K and within 2-3K of each other you should be able to rule out artifact effect of imbalanced impedances.

7. Replace any reusable electrodes especially any electrode being used for an amplifier reference or ground.

8. Are there dimmer switches in the rooms? These can commonly cause issues even if turned off.

9. And if all of these are checked and you still have the problem, talk again to your equipment vendor as they are the experts on their gear and most likely will have suggestions to help.

Good luck with resolving the problem.

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How often should gold cup electrodes be replaced with new ones? -

This varies from service to service but these are factors to consider when planning to replace a reusable gold electrode.

1. Talk to your electrodes vendor as they should be able to give an “average life expectancy." They may give the information in days (i.e., 90 days) or in patient usage.

2. Is the surface of the electrode (i.e., the gold plating) getting discolored or starting to come off due to cleaning and disinfecting? If so, plan a replacement.

3. Does the connection point between the electrode and the lead wire look worn? If so, plan a replacement.

4. Are impedances stable or are they starting to fluctuate?

5. Are you picking up a greater percent of artifact/noise?

In general, It’s up to each service when they replace and using the recommendations of your electrode provider. But my experience is many services average a replacement every 60 days, give or take a little, and depending on their patient load.

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This question is in reference to subdermal electrodes. Can these needles be taken out of sterile packaging, bundled into the appropriate EMG pop fossa or cephalic leads, put back into the electrode package for use on a patient for IOM monitoring? I understand that once the package is open one might ask if the lead is still sterile since it has the plastic needle guard on, but is this an okay practice for use? -

This is a very common practice but precautions must be taken to preserve patient safety. Certainly if you remove subdermal needles from their sterile pack, bundle the lead wires in a sterile environment, and use proper methods, you most likely have not compromised the sterility. But, if you remove electrodes from their sterile pouch and bundle them together in the tech break room on the table where everyone has been eating lunch without sterile gloves, etc., you probably have a problem.

To solve this issue, simply perform your bundling in a sterile environment using appropriate methods or you can ask your electrode provider to custom pack your specific bundles together in advance of shipment. Also, the plastic guard is really only intended to reduce needle sticks not to ensure sterility. Example of that could be if an electrode pack is opened and someone sneezes next to the needle, the cover doesn’t stop the particles from the sneeze affecting the needle.

And lastly, your risk management team or similar team is your best source for specific questions within your environment.

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How long should one soak gold plated electrodes in bleach solution to adequately disinfect, while preserving gold plating integrity of the electrode? There has not been a clear delineation of how many parts bleach to water in the bleach solution thus far, and varies from technician to technician. In addition, the time frame for soaking leads ranges anywhere from 10 or 20 minutes. -

This is a question, and protocol, that should be defined using the expertise of your risk management team. As you are correct, there are variations all over the board but it is critical that the method you are using is approved and appropriate for your testing type and requirements for medium to high level disinfecting. And, your top priority must be to adequately disinfect and your second priority is the integrity of the electrode.

If you don’t have access to a team to assist, I’d recommend considering the use of commercially available disinfecting solutions designed for medium to high disinfecting and following their directions completely. These chemicals and products can be found within a variety of supply company catalogs. Also, consult other services who have involved risk management departments and consider adoption of their policies and procedures regarding cleaning and disinfecting. This is not a topic to be taken lightly as studies have shown that improper cleaning and disinfecting can cause serious health issues to your patient population. This is one reason why many labs are shifting to disposable electrodes to eliminate this issue as cross contamination and infection risk.

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Should you use "jumpers" to fix "60Hz artifact" and/or high impedance artifact? -

No, unless you have a unique situation that this is your only option. Electrode jumpers are used to take information from one amplifier input and share it with another input. Or to average data from two or more inputs together. This is not a solution to your 60Hz artifact/high impedance artifact. You need to investigate the source of the 60Hz and bring those impedances to a balanced and low level and eliminate the use of jumpers. Jumpers can mask real problems and those real problems can mask real data that we care about. So, use with extreme caution.

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Can you point us to the definitive publication that describes the allowable error for measuring electrode placement? -

Honestly, there is no definitive publication, only guidelines. The reason for this is because each situation can be unique; so, there are guidelines, but no definitive rules. You can find guidelines in a variety of places such as the 2008 American Clinical Neurophysiology Society guidelines at www.acns.org, various references from ASET at www.aset.org, and others.

Typically the recommendation is to have your impedances as low as possible, ideally below 5kohm and within 2-3Kohms of each other. And in my experience the latter is the most important--keep your impedances within 2-3Kohms and your recording quality will most likely look good.

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What type of wires give the best impedance--gold, silver, etc? -

The type of wire isn’t the main factor of impedance. It’s really more your technique to achieve a good impedance that matters. The material on the outside of the electrode, whether gold or silver, silver chloride or tin, or whatever, is simply a conductive covering. You should be able to get a balanced impedance with any metal type. The critical points for a balanced and low impedance is good skin prep and appropriate use of the conductive material such as NuPrep, 10/20, Elefix, etc. You can survey everyone you know and you will find gold, silver, and silver chloride being the most popular metal types more because of affordability and historical preference than anything else. So choose your preference and practice good prep technique and you should be fine. But, also be aware that from vendor to vendor other factors can affect your experience with an electrode such as the lead wire type (not the metal type but what the wire is made out of). So if you decide you want to use silver electrodes be open to trying a few different versions from various vendors as the lead wire can have as much to do with your preferred electrode as the metal type.

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Hi Leah, I have a few questions for you.

I can see how a 1 cm cup electrode must have space for electrolyte; but, if we were to use the spider electrodes from Rhythmlink, what is the smallest size the wire touching the skin can be? Does Rhythmlink offer pediatric or preemie sized spider electrodes? Would it matter if one used such on adults? Can you tell us the point at which the size of the contact end of an electrode becomes useful?

2) I find that collodian, with its insulating properties, allowed the closer application of electrodes, since there was no risk of a salt bridge. However, now that we apply electrodes using the same electrolyte that is under the cup, this actually makes the active site the size of the gauge on uses, and increases the size of the electrode site (picking up more activity) and increases the possibility of coming in contact with neighboring sites. If we had a paste that was insulating, that was used on the backside of the gauze in lieu of the conductive electrolyte, this would preclude these two exigencies, and make for cleaner recordings. To your knowledge, is there an insulating electrode cream that can be used for this purpose? -

The type of wire isn’t the main factor of impedance. It’s really more your technique to achieve a good impedance that matters. The material on the outside of the electrode, whether gold or silver, silver chloride or tin, or whatever, is simply a conductive covering. You should be able to get a balanced impedance with any metal type. The critical points for a balanced and low impedance is good skin prep and appropriate use of the conductive material such as NuPrep, 10/20, Elefix, etc. You can survey everyone you know and you will find gold, silver, and silver chloride being the most popular metal types more because of affordability and historical preference than anything else. So choose your preference and practice good prep technique and you should be fine. But, also be aware that from vendor to vendor other factors can affect your experience with an electrode such as the lead wire type (not the metal type but what the wire is made out of). So if you decide you want to use silver electrodes be open to trying a few different versions from various vendors as the lead wire can have as much to do with your preferred electrode as the metal type.

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