Infants and young children present a special challenge to the Audiologist assessing hearing thresholds. Hearing impairment during infancy and early childhood leads to delays in language acquisition and impairments with speech development. Auditory brainstem response is a reliable and trusted method to accurately diagnose hearing loss during infancy and early childhood. Prior to the widespread use of ABR assessment, the average age to identify childhood hearing loss was 2 ½ years.
In 1990, the public health initiative Healthy People 2000 encouraged medical professionals to diagnose hearing loss at or before three months of age, and to initiate intervention before six months of age. This initiative was a resounding success. About 3.8 million children are born in the US every year, and 97% of them receive a hearing screening1 before one month of age.
ABR is a technology that has emerged as perhaps the most reliable method for audiologists to diagnose hearing loss in infants and young children. Having reached the 50th anniversary of the first paper on ABR, it makes sense to revisit some fundamentals of this technology. Not every audiologist receives the same level of ABR education and training. Some audiologists are trained in different methods when it comes to achieving the same measurements; but which methods achieve the most accurate, comprehensive results?
Auditory brainstem response training - what has changed?
Advances in technology now allow audiologists to perform pediatric ABR in a variety of clinical environments, and during natural sleep without the need for sedation. Information and training on the advancements in ABR technology and procedures may not be readily available for some hearing professionals. However, pediatric audiologists should be sure to familiarize themselves with the most current best practice guidelines regarding pediatric electrophysiologic measures such as frequency specific ABR, auditory steady-state evoked potentials (ASSR) and with accurate prediction of behavioral hearing thresholds based on the ABR findings.
Up-to-date auditory brainstem response training makes for better results
The audiologist may be well aware of auditory brainstem response recommendations in regards to electrode montages for adults and pediatrics. Current guidelines support alternate electrode locations for infants which are different than those for adults.
A common debate centers around high forehead vs. vertex placement. There is no significant difference in clinical results when placing the non-inverting electrode on the high forehead (Fz) or true vertex (Cz). With infants, the Fz site is preferred because it is easier to prepare the surface, there is no hair to interfere with securing the electrode and perhaps most importantly, you are avoiding the fontanel.
Similarly, placing the inverting electrode on the earlobe as opposed to the mastoid yields several benefits including avoidance of postauricular muscle artifact and easier placement of the bone oscillator when needed. Additionally, research shows that earlobe placement may result in a 30% increase in amplitude2 for wave I.
Skin preparation methods, electrode placement and the choice between disposable and reusable electrodes are important decisions for pediatric auditory brainstem response. Re-prepping the electrode sites or adjusting the positions of the electrodes on a sleeping infant is never advised, for the obvious reason of not waking a sleeping infant. Good placement and skin preparation yields lower impedance levels enhancing the audiologist’s ability to collect quality tracings.
The Joint Committee on Infant Hearing recommends that pediatric electrophysiologic assessments should include both click and frequency specific stimulation. Thoughtful planning during the assessment is important for the audiologist to tailor the test sequence based on the results collected. An initial collection comparing tracings collected with a condensation and a rarefaction click stimulus is necessary to rule out Auditory Neuropathy Spectrum Disorder (ANSD). This should be followed by frequency specific testing using tone bursts, narrow band chirp stimuli or ASSRs.
Get the latest in ABR knowledge with Natus
Here at Natus, we want to ensure that every audiologist has access to best practices for pediatric auditory brainstem response. We routinely receive questions regarding ABR usage, which protocols and methods achieve the best results and where to obtain ABR training. We have brought in a well-known and highly regarded expert to help clear things up.
1. Annual Data Early Hearing Detection and Intervention (EHDI) Program. Retrieved from https://www.cdc.gov/ncbddd/hearingloss/ehdi-data.html, November 2020
2. Update on Auditory Evoked Responses: Evidence-Based ABR Protocol for Infant Hearing Assessment, J. Hall, 2017.