Question
I have an issue with electrical noise when measuring ABRs. Do you have any suggestions on how this can be improved?
Answer
Noise during measurements can be from multiple sources. I will address the most common.
Improper gain settings - The most appropriate input gain level on the screen is equal to or less than 80 uV. Typically, recordings are made with an input gain level of 40 uV. The higher the gain, the more noise and so you should try to use the lowest gain possible without getting too many rejections.
Patient noise - This may be harder to deal with, especially when you are dealing with a child. Try to get your patient as physically and mentally relaxed as possible. Optimally, the patient should be lying down with their eyes closed, jaw muscles relaxed and if possible the patient should be sleeping.
Electrical noise - Grounding your equipment and eliminating as many possibly electrical noise sources is important. You need the patient to relax, so turn off as many lights as possible, especially neon lights. The patient may be too close to a power cord, or there may be power lines in the walls you may not be aware of. Move closer to where the patient is situated in the room if possible and avoid draping the electrode cables over any metal surfaces - such as a hospital bed railing. Always check the wall outlet for a proper ground. Many times the plug may contain a ground lead, but it is not connected to ground. Alternatively, the plug may be grounded, but it is shared with other electrical devices. This can make a dramatic difference in the amount of noise you are seeing. If you have a room that you typically perform testing in, you may need to call in an electrician to create a dedicated ground for your ABR system.
David Speidel is the director of audiology for Interacoustics USA. Beginning his career with a clinical practice and moving into sales and service, David now has over 25 years of experience in sales of diagnostic equipment. He has worked with several top manufacturers and has been instrumental in their product development, strategic planning and product support.
For more information on Interacoustics, visit https://interacoustics.com/ or their webchannel on Audiology Online