Adjusting hearing aid user's real ear performance by using probe-microphone technology
(real ear measurement, REM) has been a well-known procedure over 30 years among
audiologists. With this measurement technique, it is possible to verify whether the
output of the hearing aid at the eardrum matches the desired prescribed target. Still
less than half of audiologists verify their hearing aid fitting to match the prescribed
target amplification with this technology. Many still rely on the manufacturer's default
"first-fit" settings (initial fit approach) which means that the patient's hearing
thresholds at any given frequency are transferred to the programming software that
predicts the output and gain of the hearing aid by using proprietary or modified
prescriptive algorithm. These proprietary algorithms create an approximation over
patients in situ hearing aid gain and output based on data such as the age of the
patient, an estimate of microphone location effects, the ear mold or shell design and
length, venting size, and tubing characteristics.
Recent studies have demonstrated failures to match the prescribed amplification targets,
using exclusively the predictions of the proprietary software. The American
Speech-Language-Hearing Association (ASHA) and American Academy of Audiology (AAA) have
created Best Practice Guidelines that recommend using real-ear measurement (REM) over
initial fit approach in order to verify the prescribed gain and output of the hearing
aids. Accordingly, the recent ISO 21388:2020 on hearing aid fitting management recommends
the routine use of REM. So why is REM still rarely applied clinically? The main reason is
the lack of proof over cost-effectiveness and patient outcome. There are only few
publications of varying levels of evidence indicating benefits of REM-fitted hearing aids
with respect to patient outcomes that include self-reported listening ability, speech
intelligibility in quiet and noise and patients' preference. According to a very recent
systematic review and meta-analyses by Almufarrij et al. published in 2021, there are
only six publications that meets the inclusion criteria, and the evidence favors REM
fitting for all outcomes reported (self-reported listening ability, speech
intelligibility in quiet and noise and preference). Still, the quality of evidence varies
across the outcomes since all articles had a rather limited number of participants and
only two used power calculation to determine the sample size. None of these studies
reported health-related quality of life, which was assessed to be the primary outcome by
the reviewers. Also, secondary outcomes of interest including adverse events, generic
quality of life and cost-effectiveness were not assessed. The authors also acknowledged
the lack of sufficient follow-up duration (the maximum duration was only 6 weeks) and the
lack of permission for further adjustment to the amplification characteristics. In
addition, the included studies failed to investigate first-time users over experienced
hearing-aid users and the amplification characteristics the experienced users were
familiar with, were not reported. This was judged to possibly impact on short-term
outcomes since changes of hearing-aid users' amplification characteristics that they are
already accustomed to, can cause discomfort. The authors also claimed that future studies
should also estimate the importance of any benefit found and evaluate the reasons why
participants are reporting these benefits.
In summary, current evidence indicates that the initial fit approach often fails to
achieve the prescriptive acoustic gain and output of hearing aids, however, evidence
which would clearly show that REM-based hearing aid fitting (which is time-consuming) is
clinically relevant and cost-effective is lacking, and thus warrants further studies.
Our main research question is whether REM-based fitting improves the patient reported
outcome measures - PROMs (SSQ, HERE) and performance-based outcome measures
(speech-reception threshold in noise) over initial fit approach. These are the primary
outcomes of our study. An additional research question is whether REM-based fitting
improves hearing aid usage (self-reported & log-data report). Eventually, the
investigators will calculate the cost-effectiveness of REM-based fitting. These are the
secondary outcomes of our study.