Reflective Journals on Real Ear Measurement and Prescription Rules - Literature review Example

Real Ear Measurement Journal There are many things that audiologists need to consider during real ear measurements as new technologies are introduced. Aside from technical procedures, they need to understand the recommendations of the MHAS / MCHAS and from BSA / BAA and that one of these is that all patients should undergo real-ear measurement (REM) prior to or in their fitting appointment (BAAS newsletter, 2001). These recommendations will enlighten the practising audiologist about the available options, formulas, and procedures for measuring real ear. I have learned that the only way to view the actual performance of a particular hearing aid and ear mould on a particular patient is real-ear measurement. But patient response/opinion should also be in parallel with that of the audiologist in order to reach target. A cooperative patient will of course yield successful results whilst a patient in denial will not. A good fit is an important benefit to patients and that the use of REM recognizes the differences between coupler and real-ear measurements. In addition, patient benefit is greater when the target is well-matched. The baseline measure is useful when the patient will want to change aid later on. REM also shows the effects of fine tuning and provides graphical confirmation to the audiologist that the intended prescription/processing strategy have been implemented by the hearing aid software. Real ear measurement ensures the audiologist will be able to understand the whole process. REM is also helpful during counselling of patient and their family members about what they can and cannot hear. It will verify the function of advanced features like directional microphone and even noise reduction features. Therefore, the audiologist should be adept about REM. Adult and Children During the lectures and readings, I also learned considerations for adults and children patients due to different approaches to real ear measurement. It was suggested that normal hearing in infants are uncertain (Ching et al, 2001). There are also acoustical differences between the ear canals of children and adults that affect the audiometric data as well as the hearing aid amplification. The audiologist should be aware of this when faced with a child or adult patient. To minimize or eliminate mistakes in prescribing amplification, the audiologist should base thresholds in sound pressure level at the tympanic membrane. Measurement errors are seen to be fewer for adults, especially those with average ear canal size and resonance. Children are also more restless during probe tube insertion for longer periods so the audiologist should be patient with the child. Real-ear Insertion Gain (REIG) or Real-ear Aided Response (REAR) In choosing between REIG and REAR, placement of the probe tube is seen to be less critical in REIG than for REAR. Dillon (2001) also noted the increase in SPL at the tympanic membrane is measurable at a mid-canal point when the probe is in the same place for the unaided and aided conditions of the REIG procedure. New audiologists or those with limited experience of probe tube measurement benefits from this due to less complication. REIG is most common but not recommended for adults with abnormal middle ears (Dillon, 2001). REAR is method of choice in DSL i/o and for children although still useful for adults. Prescription Keidser et al (2003) suggested that a choice of generic is practical rather than manufacturer-specific aid. This will have the patient avoid the difference they might experience when changing aids from one brand to another. During the update of patients’ DSP aids, it is possible that patients will change from one brand or manufacturer to another. This is why generic aids should be recommended as it will be beneficial for both patient and clinician. NAL & DSL Prescription rules are provided audiologists today as a guide in order to achieve targets or goals for patients. As mentioned earlier, patient-centeredness will provide the most benefit results. In NAL, equally loud frequency elements of speech must be achieved. This will lead to effective audibility. When compared against DSL, there is less high-frequency gain and output in NAL. The formula also has a speech-o-gram option and can be applicable for REIG or REAG. DSL on the other hand has a goal to achieve vowel and consonant combinations and will be helpful for children who are learning language. A comfortable loudness for each frequency range is also achieved, although equal loudness is not a priority (Harley, 2011). The preferred prescription target for adults is NAL-NL1 according to Moore et al (2001). From some hearing losses, it was noted that DSL i/o prescribes more high frequency gain than preferred among adult patients. For children, preference is DSL i/o but children fitted to NAL-NL1, REAR must be used instead of REIG. The reason is that REIG targets are based on average adult ear canal resonance and inappropriate for children. Children usually have higher frequency ear canal resonances than the adult patients (Valente et al, 2008). In choosing between the two formula, the audiologist will need to consider the priority of the patient in order to determine which formula will be best. Use of inappropriate target can lead to under-amplification in the mid frequencies. Using REAR also allows visualization of all relevant variables such as the decision to “under amplify” relative to targets and the only way to check that speech remains audible (British Society of Audiology, 2007). Setting up the Equipment This portion of the lecture is equally important. The first step to set up is to load the proper software defaults. The audiologist should take note of the stimulus type and display parameters. In addition, the audiologist should check the hardware configuration. When measuring RECDs, the audiologist should ensure the positioning of coupler and reference microphones. For a clinic that provides paediatric and adult service for its REM equipment, it is advised that they set up different files for default settings fit for each clinic (Valente et al, 2008). Ambient Noise and Environment REM should be done in a sound-attenuating booth but a quiet room is more conducive where the ambient noise will not affect the test results by more than 1 dB at any frequency. Large, reflecting surfaces such as a table should be stored away from the loudspeaker and the patient. 1 meter distance from reflective surface is desirable. A loudspeaker facing the centre of the room is most preferable set up. If the loudspeaker is set on a wall, it should be 1 m away from the corner (Valente et al, 2008). Calibration Full objective calibration within the last 12 months is required for REM equipment. They also must comply with BS EN 61669. Portable equipment moved to different locations must be calibrated every 3-6 monthly intervals or more if the microphone has been dropped (Valente et al, 2008). Measurement systems for real-ear usually involve calibration of the probe tube before conducting measurements. This is because probe tube calibration is responsible for the acoustic effects the probe tube creates as sound travels through it when placed in the ear canal. It goes to the probe microphone during actual use conditions. Calibration clears the acoustic effects the probe tube and microphone creates during real-ear measurement. In careful and accurate calibration process, the probe tube and the microphone is made acoustically invisible (Valente et al, 2008). Preparing a patient For a child patient, careful placement of the probe tube should be observed and new probe tube is recommended for every patient. Thinner probe tube is also applicable in order to reduce discomfort for the child as the audiologist touch the canal wall or tympanic membrane (British Society of Audiology, 2007). The audiologist should attach a short ruler to the top of the REM equipment before probe tube is inserted down the ear until the marker is at the tragus. This will facilitate a faster measurement. The audiologist is then advised to use an otoscope to ensure that the probe-tube is lying along the bottom of the canal or at least 5mm beyond the end of the ear mould tip. This will delete standing wave effects (British Society of Audiology, 2007). Coupler-derived REAR measurement The audiologist will couple the hearing aid to the coupler using a length of tubing carefully. The tubing is the same as the ones used for a BTE fitting. Then, the audiologist will need to ensure that the appropriate target has been set in the REM software as well as having the correct measurement mode. He will then select either measure RECD or predicted RECD depending on which measurement is used. When switching the hearing on, the usual listening programme features should be used, with the highest acclimatization level and the proper vent size (Valente, 2008). Using RECD It was suggested that RECD is a powerful tool helping audiologists throughout the various stages of the amplification process – from the hearing instrument fitting methods using the SPL-O-GRAM format, and converting real ear targets to cc coupler targets as audiologist consult manufacturer’s specification. RECD predicts real-ear output when measuring hearing instruments in the 2cc coupler. It guides audiologist to know the difference between output in the real-ear and the 2cc coupler. In addition, it provides accurate prediction for real-ear hearing aid output within approximately 2 dB (Valente et al, 2008). It would then benefit audiologists to consider the RECD technology in their clinic. In predicting hearing instrument output, the various advantages gained by audiologist include knowing the levels of amplified sound delivered into the patients ear canal, proper accounting for the unique acoustic properties of the ear and ear mould properties in order to minimise errors; the hearing instrument response shaping can be undertaken in the hearing aid test chamber with highly controlled acoustic conditions; and cooperation and time from the patient in the fitting process is reduced (Valente et al, 2008). This provides ease not only for patients but also for the audiologist for proper diagnoses and ear measurements. In-situ REAR Approach In the conduct of in-situ rear approach, it is best that the child patient is seated so that the ear under test is about 45° to the loudspeaker. It should be anticipated that young children being tested to Visual Reinforcement Audiometry will react to the loudspeaker by moving their head. They should be given a distraction like a catchy photograph on the wall and positioned at 0° azimuth and seated 0.5 m from the loudspeaker with the same level with the centre of the loudspeaker instead of the cabinet (Keidser et al, 2003). REAR measurement In measuring non-linear hearing aid, the audiologist should carefully insert the earmould and hearing aid into the patient’s ear steadying the probe tube. Ensure that the appropriate target has been set in the REM software and that the correct measurement mode is in place (Moore et al, 2001). When the hearing aid is in place, the marker should be at the tragus. And then the audiologist will input 65 dB SPL modulated speech-shaped noise stimulus and record comparing with the 65 dB SPL target. The audiologist should take note of any frequencies where the response changes substantially from the target. For the experienced audiologist, it is alright to increase the input level to 80 dB SPL and then 50 dB SPL to note the changes. It is also advisable that increase of the intensity in steps from 65 dB SPL instead of straight up to 80 dB SPL in order to avoid discomfort of patient (British Society of Audiology, 2007). I noted that patient discomfort should be avoided to ensure quality output. Modifying the Programming in the Aid This is performed on the coupler or in-situ but the audiologist should check when a coupler-derived approach was used that the REM system is in coupler mode. Incorporating any measured RECD data into the hearing aid software may improve the accuracy of the first auto fit. Adjust the hearing aid software to match targets at all input levels. Separate adjustments for soft input levels and loud input levels are usually done. Adjustments to the aid should be done while the signal level in the REM system is running in order to note the modification. Some combinations of software and hardware may not be possible and staff should seek advice from hearing aid suppliers (Baumfield and Dillon, 2001). The audiologist who fails to match targets at all inputs levels should compromise matching all three targets. Dillon (2001) said that children acquiring language may benefit from more precise matching of soft speech targets. In addition, matching the very loud target avoids exceeding the uncomfortable loudness level. The audiologist should ensure that output does not exceed uncomfortable loudness levels as it is preferable to adjust the MPO in a controlled way in the clinic to avoid discomfort for patients outside the clinic. The Noise Risk Criteria set by the Physical Agents Directive must be balanced for every child patient against the clinical benefits (Keidser & Brew, 2003). The various considerations of the audiologist during real ear measurement are many. However, I have learned the need to consider the patient first, as well as the patient’s welfare after stepping out of the clinic. Proper and accurate measurement will not only benefit the patient during the measurement process but also provide satisfaction for service by the clinic. It is therefore important to take heed of all the steps and necessary tests inside the clinic during measurement process to ensure that proper procedures, options, formula, and measurements were implemented. References BAAS newsletter, 2001, issue 36 British Society of Audiology. 2007. Guidance on the use of real ear measurement to revify the fitting of digital signal processing hearing aids. Accessed from http://www.thebsa.org.uk/docs/RecPro/REM.pdf Baumfield, A & Dillon, H. 2001. Factors affecting the use and perceived benefit of ITE and BTE hearing aids. Br J Audiol. 35, 247-58. Ching, T.Y., Dillon, H & Byrne, D, 2001. Children’s amplification needs-same or different from adults? Scand Audiol Suppl. 2001 (53). 54-60. Dillon, H. 2001. Hearing Aids. Chapter 4. Electroacoustic Performance and Measurement. Boomerang Press. Harley, B. 2011. Prescription rules & Clinical outcomes NAL & DSL. UCL. Keidser, G., Brew, C. & Peck, A. 2003. How proprietary fitting algorithms compare to each other and to some generic algorithms. Hearing Journal, March, 28-38. Moore, B. C. J., Alcantara, J. I. & Marriage, J. 2001. Comparison of three procedures for initial fitting of compression hearing aids. I experienced users, fitted bilaterall. Br J Audiol 35, 339-353. Valente, Michael , Holly Hosford-Dunn, Ross J. Roeser, 2008 2nd ed. Audiology treatment. Thieme. Read More