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Parent Category: Clinical Applications

Category: Hearing Screening

Last Updated on Saturday, 29 December 2012 14:40

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In these pages we would like to present information (i) for screening programs who have started recently their activities; or (ii) for groups who want to start a screening program in the near future.

1. What are the stages of an efficient screening program :

Experience has shown that the best way to implement an UNHS program (universal screening = Well babies and NICU residents) is to follow a three-stage protocol.

In stage one (within 48 hours of life) the subject is tested by OAEs (DPOAEs or TEOAEs) .

If the test results in REFER (caused by high ambient noise, or due to the fact that the subject is agitated and no recording is feasible) another OAE test is performed within one week from the first. The second retest is reffered to as the second stage.

In case that the outcome of the second stage is still a REFER, the subject is scheduled for an Auditory Brainstem Response session (third stage) within a max period of three months from the second OAE test.

It should be noted that the testing times depend on the local or State maternity-hall regulations. An Efficient program should COVER at least 95% of the available population.

The timing and the testing procedures of the above protocol apply primarily to well-babies. NICU (Neonatal Intensive Care Unit) infants are tested prior to dismisal at a PCA (post conceptual age) age > 35 weeks. It is common to test the NICU infants with OAEs and AABR to identify latent /emerging cases of Auditory Neuropathy (AN). Well-babies are not tested routinely for AN, for a variety of reasons the most important being the lack of time and financial resources.

2. What is the best OAE-generation technology to use:

The earlier OAE-generation equipment was geared for both neonatal screening and clinical research. The latest devices target only neonatal screening, cost less and there are easier to use.

ATTENTION:

It should be mentioned that the manufacturers of the portable screening devices are not always offering the necessary software (database) for the proper storage of the acquired recordings. In this context, in clinical environments were multiple exams are conducted per day, it is very probable that errors will occur in the codification of the data (relating a recording to a particular name).

3. What is the best type of OAE to use:

For screening purposes both TEOAEs and DPOAEs convey the same information . Estimates at the frequencies of 2.0, 3.0 and 4.0 kHz have been established as good descriptors of a healthy peripheral function. DPOAEs might offer an advantage in noisier environments, due to fact that the DPOAE stimulation scheme is more efficient.

ATTENTION: The fact that a subject has acceptable OAE responses at the tested frequencies (a PASS case) does not IMPLY automatically that the subject CAN HEAR.

4. Which OAE protocol is employed more often in clinical practice:

This information refers to first and second generation devices mostly, because the third generation equipment use pre-loaded OAE protocols.

For the TEOAEs it is very common to use the QuickScreen modality (12.5 ms recording window ) with a 80- 84 dB SPL stimulus (non-linear click train , that is 3 positive clicks followed by a negative one which has an amplitude three times the value of the positive click). The QuickScreen protocol was mainly developed during the RIHAP project and represents a significant evolution of the initially developed nonlinear protocol (20.48ms recording window).

Editor's Note: The term "nonlinear" used to describe the "3 +1" click train is somehow misleading because it is not related to a nonlinear-stimulus. It is assumed that when the cochlea is stimulated by clicks having an intensity 80-84 dB SPL the cochlear response is saturated. In this context, the addition of the positive and negative clicks eliminates the linear contributions of stimulus artifacts . It should be noted that this "cochlear scenario" is valid only for adult subjects but not for neonates. Linear protocols (the click-train is composed by 4 clicks of the same polarity) are used mainly in suppression studies . Linear protocols (20 ms recording window) can be used in screening but the employed stimuli should not exceed the intensity value of 75 dB SPL . The responses should be windowed in order to suppress occasional artifacts. Usually a 3.5 - 12.5 ms window works sufficiently for well-babies and NICU residents.

For the DPOAEs it is common to use a 65-55 dB SPL asymmetrical protocol. To compensate the presence of ambient noise higher stimulus protocols can be used as the symmetrical 70-70 or the asymmetrical 75-65 dB SPL. Above the stimulus intensity of 65 dB the asymmetrical protocols lose their efficiency , which means that both symmetrical and asymmetrical protocols evoke similar responses.

5. How to judge if the acquired OAE responses as normal (screening criteria)

This information refers to first and second generation devices mostly, because the third generation equipment use pre-loaded OAE protocols with pre-specified screening criteria.

Until today there is no consensus on the screening criteria or their corresponding values. Experience has shown that it is better to divide the evaluation of the responses into two categories : A PASS or a REFER. For the TEOAEs the majority of the UNHS programs utilizes as indicators the values of the S/N ratio , or the TEOAE reproducibility at the frequencies of 2.0, 3.0, and 4.0 kHz.

For a PASS the reproducibility at ALL three frequencies should be higher than 75 % and the S/N ratios higher than 6 dB.
For the DPOAEs the screening criteria are protocol dependent (The 65-55 is considered as the default option). Usually the DPOAE S/N values are estimated at 2.0, 3.0and 4.0 kHz and if ALL three are higher than 5-6 dB the case is assigned as a PASS.

For users of first or second generation OAE instruments it is highly recommended the construction of a local normative estimate from a number ( > 200) of well-babies, which can be used to describe the values of the normal OAEs .

6. Which type of OAE is more frequency specific:

This issue has caused a lot of confusion in the OAE community, due to the background we have in Auditory Brainstem Responses. In ABR a click stimulus is not frequency-specific, where tone-bursts and tone pips are. Extrapolating this information in the OAE field one might erroneously consider that the TEOAEs have no frequency-specificity, while the DPOAEs are frequency specific.TEOAEs are frequency-specificbecause the cochlea is tonotopic. The DPOAEs are NOT more frequency-specific than the TEOAEs, according to a number of recent studies which have shown that the cubic distortion DPOAE responses, we use in clinical practice, are composed from two components one "distortion-generated" and one"reflection-generated".

7. Does the presence of auditory neuropathy / dysynchrony cases (not detected by the conventional OAE screening protocols) compromise the hearing screening efficiency ?

A 100% detection of all the hearing loss (HL) cases in a given population, is more of a theoretical objective
than an actual clinical reality. The methodologies we use in the detection of hearing impairment are subject to a number of constraints resulting in numerous compromises (i.e correct number of normal subjects identified vs correct number of HL cases identified etc). In theory a program with infinite financial resources could develop policies to detect with a high accuracy all cases of interest (normal and HL), but such a objective is far away of any clinical reality in our-days. The presence of undetected auditory neuropathy cases is a "stigma" for the neonatal hearing screening and early intervention programs, but these programs represent the best we can do under our financial and time constraints.

Multimedia Resources

Recent examples (released in 2002-2003) of Multimedia CDs for the classroom are the following :

Infant Hearing Screening: Education and training CD (2003), by Gn-Otometrics. The material focuses on the application of the AccuScreen neonatal screening device, but there are many generic examples on screening practises and the auditory periphery. If you are interested in obtaining a copy, contact us so that we can forward your request. 

A Better Understanding of Hearing: (2002) Contains information many practical issues for undergraduate classes in Audiology. OAE practitioners will find nice videos showing the movements of the OHCS. If you are interested in obtaining a copy, contact your local Oticon / Widex dealer or the information desk of Oticon.

A Promenade tour around the Cochlea (2002). This is the CD version of the web-site created by Remý Pujol, and represents an excellent multimedia material for Hearing Science and Audiology students. If you are interested in obtaining a copy, contact us so that we can forward your request.