RECDs: Tips and tricks for getting a good measurement

This video demonstrates some suggestions to help when performing real-ear-to-coupler difference (RECD) measurements. You can read the full transcript below.

Probe microphone insertion

With both REMs and RECDs, probe microphone insertion is often the most daunting part of the process. Making use of the SPL60 probe simplifies this step, as there is only one object to insert into the patient's ear, with the probe microphone built into the probe, making it a very easy and quick way of achieving an accurate measurement.

However, when using the patient's own ear mold, or an insert foam tip, it is necessary to insert the probe microphone alongside either of these. This can be a somewhat fiddly process made more challenging if there is some patient movement and by the small ears of pediatric patients.

Firstly, it is important, as with REMs, to ensure the probe microphone is marked to the correct length for insertion. For pediatric patients, it is recommended to insert the probe microphone a few millimeters beyond the end of their ear mold, the SPL60 probe, or the foam tip.

The SPL60 probe accounts for this with its design. However, when using an ear mold or foam tip, you should position the probe microphone alongside, a few millimeters beyond the end, and move the black marker so that it is in line with the outer edge of the ear mold or foam tip.

Once the correct probe microphone length has been established and marked, you are ready to insert the probe microphone into the ear canal. Here, there are two ways of doing this, each with their own advantages.

You can insert the probe microphone into the ear canal on its own, followed by the ear mold or foam tip, as you would do for performing real ear measurements. This is a two-step process but benefits from being easily adjustable, should the probe microphone need re-placing if the measurement is not deemed appropriate.

Alternatively, you can attach the probe microphone to the ear mold or foam tip. You can do this by using a small strip of micropore tape to wrap around the ear mold or foam tip with the probe microphone alongside it. Be careful to ensure the probe microphone remains in the correct position for the appropriate length.

Or, you can cut a small strip of clingfilm (cellophane / saran wrap) and wrap this around the ear mold or foam tip, connecting the probe microphone to it. Some clinicians also choose to then apply some lubricant to the outside of this setup in order to ease insertion.

This way you have only one combined object to insert into the ear. But this does require a bit more preparation and is less easily adjustable if the probe microphone needs replacing.

Results management

Once you have completed your measurement, the software will display the coupler measurement, the ear measurement, and the RECD value, which is the difference between the two.

You are then ready to perform your hearing aid verification in the coupler. However, it is important to inspect your RECD to ensure that it is a good quality measurement. A good RECD should be above 0, largely positive, focusing on the area up to 8 kHz.

It is also possible to compare the RECD against predicted RECD data, which is based on average measurements across a larger number of patients. In order to do this, you can ask the Affinity Suite to display the predicted RECD on the opposite ear to the one you have measured, and then select binaural view to see them overlaid.

Here we can see a good correlation between our left sided measured RECD and the predicted RECD shown in red. This can provide a useful comparison. However, individual variations are to be expected, particularly if there are middle ear abnormalities such as negative pressure effusions or PE tubes.

Option to transfer results from one ear to the other

The gold standard of RECD measurements is to perform the measurement in each individual ear. However, this is not always possible due to patient cooperation. Therefore, it is possible to perform the measurement in one ear and copy it across to the other. This should only be performed when the anatomy and middle ear function of both ears is similar.

To copy the measurement to the opposite ear, you can right click on the measurement in question, which is a left sided RECD in this case, and select "Transfer to right ear". Then when the right ear is selected, you will see the left sided RECD has been copied over but is still displayed in the original color to make it clear which side the measurement was performed on.

You can then verify the right sided hearing aid using the left sided RECD.

Predicted RECD

Sometimes it isn't possible to record an RECD at all. This can happen for a number of reasons. For instance, perhaps the patient is not sufficiently cooperative or maybe there is excessive wax in the ears, or they present with an ear infection on the day of the measurement.

In these cases, it is possible to use the predicted RECD by clicking on RECD for the ear in question and selecting Show predicted RECD. This can then be used for the verification process.

How to use a previously measured RECD

Another option in these circumstances is to use a previously measured RECD for that patient. Although this won't be as current as a newly measured RECD, it is considered more accurate than using predicted RECD measures.

To use a previous RECD, you can select the previous session where the measurement is saved, right click on the measurement in question, and select Transfer to current session. If you then return to the current session, your previously measured RECD has been applied ready for verification of the hearing aid.