Introduction

A pediatric audiologist’s main role is to identify and treat childhood hearing loss as young as possible. To do so, conventional testing techniques must be adapted to accommodate to the developmental level of the child. This chapter will review ways to identify hearing loss at a very young age and will describe specialized techniques used with children.

As children are continually developing, the successful pediatric audiologist is required to monitor development as well as diagnose and treat hearing loss. This includes tracking speech and language development, supporting academic accommodations, monitoring emotional and social development, educating parents on these topics, and referring to other specialists when concerns arise related to learning difficulties, cognitive delays, and/or motor delays. The pediatric audiologist works as a part of a multidisciplinary team to best serve children with hearing loss.

Pediatric audiologists have special training in child development, counseling, behavior management, and pediatric specific testing techniques. Most pediatric facilities work with patients from birth through 18 to 21 years of age. Many pediatric facilities will continue to serve patients into their adult years if a significant developmental delay prevents the individual from participating in adult testing techniques.

What Is Universal Newborn Hearing Screening?

Newborn infant hearing screening (NIHS) was recommended by National Institutes of Health consensus in 1993. ¹ The concept gained traction when supported by a position statement from the American Academy of Pediatrics in 1999. ² In 2007, the Joint Committee on Infant Hearing recommended that infants be screened for hearing loss by 1 month of age. If an infant refers on the screening, he/she should be referred for a diagnostic evaluation that is to be completed by 3 months of age. If hearing loss is identified at the diagnostic evaluation, the infant should begin intervention by 6 months of age. ³ As of 2008, 43 states have legislation requiring NIHS. ⁴ Although each state’s requirements differ, the Center for Disease Control (CDC) reports that in 2013 more than 90% of babies born in the United States were screened for hearing loss by 1 month of age and by 3 months of age greater than 95% had been screened. Screening tools and protocols vary from center to center; although, commonly used screening tools include automated auditory brainstem response (AABR) and otoacoustic emissions (OAE) testing ( Figs. 5.1 and 5.2 ). Depending on the testing protocol that is implemented, the sensitivity and specificity of the screening can vary. For example, if OAE testing is the only screening used, neural hearing losses will be missed (i.e., hearing loss secondary to deficient auditory nerve or auditory neuropathy spectrum disorder). Regardless of the chosen screening tool, it is accepted that the screenings will miss the detection of mild hearing loss, sloping hearing loss when normal to mild hearing thresholds are present between ~1,000 and 3,000 Hz, and progressive hearing losses that worsen with time. Expected referral rates differ depending on the nursery level (i.e., well baby nursery versus neonatal intensive care unit [NICU]). For example, a well-baby nursery should have a refer rate between 0.5 and 2%, whereas a NICU may be near 10%. When combining across nursery levels, an overall refer rate of 4% is expected. ³

The goal of NIHS is to identify hearing loss at a very young age to provide intervention prior to the child falling behind in language development. To this end, most states have early intervention programs that monitor the screening data and support intervention resources (early hearing detection and identification). While national data suggest that newborn hearing screenings are successfully being implemented, the CDC reports that ~40% of the babies who are referred for diagnostic evaluation based on newborn hearing screening are lost to follow-up. ⁴ State programs are partnering with health professionals to improve this statistic.

What Are the Risk Factors for Childhood Hearing Loss?

There are many risk factors associated with childhood hearing loss. Children with one or more risk factors should be referred for audiologic evaluation by 12 months of age and be closely monitored, even if they passed their NIHS. Parents should be made aware of these risk factors and counseled on the importance of follow-up care. Early identification is necessary to ensure that these infants receive medical intervention, hearing assistive devices, and access to therapeutic services as soon as possible. The following risk factors have been identified by the U.S. Department of Health and Human Services Centers for Disease Control and Prevention ⁷ :

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  Caregiver concern regarding hearing, speech, language, or developmental delay.

  
  
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  Family history of permanent childhood hearing loss.

  
  
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  NICU stay of more than 5 days or any of the following regardless of length of stay:

  
  
  
  
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    Extracorporeal membrane oxygenation

    
    
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    Assisted ventilation

    
    
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    Exposure to ototoxic medications (gentamicin and tobramycin)

    
    
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    Loop diuretics (furosemide/Lasix)

    
    
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    Hyperbilirubinemia requiring exchange transfusion

  
  
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  In utero infections, such as cytomegalovirus, herpes, rubella, syphilis, and toxoplasmosis.

  
  
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  Craniofacial anomalies, including those involving the pinna, ear canal, ear tags, ear pits, and temporal bone anomalies.

  
  
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  Physical findings, known to be associated with a permanent or conductive hearing loss. (e.g., a white forelock is associated with Waardenburg syndrome, which is associated with permanent hearing loss).

  
  
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  Syndromes associated with hearing loss or progressive or late-onset hearing loss, such as neurofibromatosis, osteopetrosis, and Usher syndrome. Other frequently identified syndromes include Alport, Pendred, and Jervell and Lange-Nielson.

  
  
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  Neurodegenerative disorders, such as Hunter syndrome, or sensory motor neuropathies, such as Friedreich ataxia and Charcot–Marie–Tooth syndrome.

  
  
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  Culture-positive postnatal infections associated with sensorineural hearing loss, including confirmed bacterial and viral (especially herpes viruses and varicella) meningitis.

  
  
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  Head trauma, especially basal skull/temporal bone fracture requiring hospitalization.

  
  
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  Chemotherapy.

  
  
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  Middle ear disorders such as:

  
  
  
  
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    Otitis media

    
    
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    Cholesteatoma

    
    
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    Tympanic membrane perforation

  
  
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  Acoustic trauma.

When Should Children Have Hearing Screening Beyond NIHS?

In addition to NIHS, children (even those without risk factors for hearing loss) should be screened for hearing loss throughout childhood to capture acquired hearing loss that was not present at birth. The American Speech–Language–Hearing Association (ASHA) ⁸ recommends a hearing screening schedule for school-age children as follows:

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  Entry to preschool (~ 3 years of age)

  
  
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  Annually from kindergarten through third grade (~ 5–9 years of age)

  
  
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  Seventh grade (~ 12–13 years of age)

  
  
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  Eleventh grade (~ 16–17 years old)

What Test Methods Are Used to Evaluate Infant Hearing?

The ASHA recommends that the testing of infants (birth to 5 months of age) should rely primarily on physiologic measures of auditory function. ⁸ These measures include ABR (Chapter 2) using frequency-specific stimuli to estimate the audiogram, OAEs, and acoustic immittance measures (Chapter 2). ⁸ , ⁹ It should be noted that while conventional tympanometry (using a 226 Hz probe tone) is an effective tool in identifying middle ear dysfunction for children and adults (Chapter 2), high-frequency tympanometry (using a 1,000 Hz probe tone) has been proven to more accurately identify middle ear pathology in infants less than 7 months of age. This has been attributed to the acoustical and anatomical properties of the infants’ external and middle ear system. ¹⁰ While OAEs and ABR can provide an objective estimate of hearing sensitivity, these diagnostic tests do not provide a direct measure of functional hearing abilities. ⁹ Therefore, behavioral hearing testing should always be attempted once the child is developmentally able to participate.

By 6 months developmental age, most infants can be conditioned to provide a behavioral response when an auditory stimulus is presented. Indicators that a child is ready for this type of testing include being able to sit up mostly unassisted and looking around the environment with curiosity. Visual reinforcement audiometry (VRA) is a diagnostic procedure used to evaluate hearing in infants between 6 and 30 months of age ( Fig. 5.3 ). The infant is conditioned to turn his/her head toward a reinforcer (i.e., a toy/animal that lights up; a short video clip) each time the auditory stimulus is presented. Stach and Ramachandran ⁹ outline how this procedure is completed:

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  Seat child in high chair, in a child’s chair, or on a parent’s lap.

  
  
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  The test assistant or parent keeps the child’s attention facing forward using quiet toys.

  
  
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  The auditory stimulus is presented at a comfortably loud level above expected threshold. The auditory stimulus and conditioning/reinforcing toy remain on simultaneously for 3 to 4 seconds.

  
  
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  Step three is repeated until the child consistently turns to the auditory stimulus.

  
  
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  When the child is conditioned to respond, the auditory stimulus is presented without activating the conditioning/reinforcing toy. If the child turns toward the sound, the reinforcing toy is activated and conditioning is complete.

  
  
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  Testing proceeds to obtain hearing thresholds for one low (500 Hz) and one high (2,000 Hz) frequency stimulus. The stimulus is decreased until the child stops responding and is then once again increased to bracket threshold.

  
  
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  Additional frequencies to be tested will be determined by the response to the initial frequencies tested.

  
  
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  Testing can proceed using insert earphones, bone vibrator, and hearing assistive technology (hearing aids, cochlear implants [CI], and frequency modulated [FM] systems).

  
  
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  The reinforcing toy is activated only when the child makes a conditioned head turn to a sound. When in doubt, do not activate the reinforcer.

A test assistant or centering toy is critical in making sure the infant’s attention is focused forward before the audiologist presents the stimulus so a head turn can be observed. It is also important that the infant’s parent does not cue the infant when the auditory stimulus is presented. If this is observed, the test assistant or audiologist provides further instruction to the parent.

While testing in the sound-field is often necessary in the pediatric population due to limited acceptance of headphones or insert earphones, there are several considerations requiring attention. These include controlling and calibrating the test environment (minimizing ambient noise levels and positioning the patient at a calibrated location that takes into account distance and angle in relation to the loudspeaker, avoidance of standing waves) and interpreting results with caution due to the lack ear specific information. Sound-field testing must take place in a sound treated booth to minimize the ambient noise. Additionally, the space must be large enough to minimize the effects of reverberation and standing waves, which can invalidate results.

“In a reverberant space, the sound perceived by a listener is a combination of direct and reverberant sound. The ratio of direct sound is dependent on the distance between the source and the listener, and upon the reverberation time in the room. At a certain distance the two will be equal. This is called the ‘critical distance.’” To further reduce the risk of standing waves, it is necessary to use warble tones or narrow band noise rather than pure tones during sound-field testing. ¹² In addition to distance, the child’s angle in relation to the loudspeaker must also be calibrated and observed during testing. Most commonly the child is either facing the speaker (0 degrees azimuth), or the speaker is off to the right or left of the child by 45 or 90 degrees azimuth ( Fig. 5.4 ). Therefore, it is crucial that the patient is positioned correctly in the sound booth at the “critical distance” and calibrated angle to the loudspeaker to provide the accurate threshold level the patient is responding to.

It is also important to recognize that auditory thresholds obtained in the sound-field are not a reflection of the softest sounds a child can hear, but are actually the softest sounds a child can detect against the background noise in the test environment. ¹⁴ As a result, the American National Standards Institute (ANSI) has created standards specifically addressing maximum permissible ambient noise levels for testing to audiometric zero. For details, refer to the ANSI standard for maximum permissible noise levels (ANSI 3S1–1999) and the ANSI standard for audiometric zero is ANSI S3.6–1996 (ANSI). ¹⁵

While sound-field audiometry can provide valuable information regarding hearing sensitivity, it is impossible to discern ear specific information without the use of headphones or insert earphones. When thresholds are obtained in the sound-field, it should be known that those thresholds represent the better hearing ear. When headphones are not tolerated, parents are encouraged to practice wearing headphones with their child at home to help increase acceptance for future testing.

What Test Methods Are Used for Toddlers and School-Aged Children?

Conditioned play audiometry is a diagnostic technique used for children with a developmental age of 2½ to 5 years ( Fig. 5.5 ). By 2½ years of age, children can be conditioned to perform a motor task in response to a stimulus (i.e., drop a block in a bucket or put a ring on a stand when he/she hears a sound). ¹⁶ Some children will be able to participate in this method of testing slightly younger; however, reliability of responses may decline or attention may fatigue prior to the completion of an audiogram. At over 5 years of age, the child can participate in conventional audiometry, which consists of the child raising his/her hand or pushing a button in response to a tonal stimulus (Chapter 2).

For younger children, testing often begins in the sound-field (i.e., using loudspeakers) since headphones may not initially be accepted. The stimulus is presented at a level that is easily heard by the child to reinforce the response. “Hand-over-hand” is a technique that is used to condition children. The test assistant will put a toy in the child’s hand and place his/her hand over the child’s hand. When the stimulus is presented, the assistant will say, “We heard it, we put it in,” and move the child’s hand to perform the task (i.e., dropping a block into a bucket). The assistant will continue hand-over-hand until the child starts to respond independently when the stimulus is presented. ¹⁶

Many times a speech awareness threshold (SAT) will be the first measure obtained since children condition most easily to a speech command (i.e., “put it in”). An SAT is the lowest intensity level in dB HL that the child can detect a speech stimulus for at least 50% of given presentations (it does not indicate recognition of the words/sounds spoken). For older children, repeating spondee words (i.e., two syllable words with equal stress on each syllable; includes such words as baseball, cowboy, hotdog, etc.), or pointing to the picture of a word that was presented can also provide a speech recognition/reception threshold (SRT) ( Fig. 5.6 ). An SRT is the lowest intensity level in dB HL that the child can repeat the spondee word correctly for at least 50% of given presentations. Test order will vary depending on the suspected type of hearing loss. For example, for a child suspected of having a conductive hearing loss (i.e., abnormal tympanometry results), responses to a high-frequency tone (such as 2,000 Hz) should be obtained, as low frequencies are more impacted by the presence of otitis media. Once a high-frequency threshold is obtained, a low frequency is then evaluated (500 Hz). If sensorineural hearing loss is being ruled out (i.e., normal tympanometry), a low-frequency tone may be attempted first, since hearing tends to be better in the lower frequencies. ¹⁶ The audiologist then needs to determine what test information is most valuable to obtain. If a loss is identified via air-conduction testing at a low and high pitch and cooperation is a concern, the audiologist may choose to pursue bone-conduction testing prior to obtaining more pitches via air conduction to ascertain the type of hearing loss. If continued participation is not a concern, the audiologist will need to assess how likely the patient will tolerate headphones or insert earphones to pursue ear-specific information.

Frequencies 500 to 4,000 Hz are the primary focus, as those frequencies carry the majority of important speech information (250 Hz and 8,000 Hz are also tested if the child is still providing reliable responses). For younger children, the audiologist may choose not to present the stimulus below 10 and 15 dB HL (i.e., level of normal hearing). It is important to obtain as much diagnostic information as possible before the child fatigues. If the audiologist is consistently obtaining responses at 10 to 15 dB HL, the child’s hearing is considered normal at that frequency and another frequency can be evaluated. For older compliant children, headphones may be placed at the start of testing and hearing thresholds can be obtained at each ear. While the goal is to obtain ear-specific information, if the child has an adverse reaction to headphones, testing can be completed in sound-field. Determining hearing sensitivity for at least the better ear provides important information, especially for a patient population first acquiring speech and language skills. If hearing is normal for at least one ear, that is adequate for speech and language development to begin. ¹⁹

In addition to pure-tone audiometry, speech audiometry should also be evaluated beyond an SAT or SRT. Speech perception measures include the presentation of 25 to 50 developmentally appropriate words at an intensity level that is loud but comfortable (typically ~ 40 dB above the child’s SAT or SRT). These words are presented sequentially to the child who either chooses the correct word from a set of four to six pictures (closed set) or repeats the word (open set) if speech production is intelligible. Speech perception measures allow the audiologist to quantify the clarity of speech sounds via percent of correctly identified words or phonemes (individual speech sounds) and provides additional information beyond audibility of sound. Speech perception measures should be obtained on all children and are critical for any child identified with a sensorineural hearing loss to help determine appropriate options for amplification. ⁹ If, however, tympanometry and the air conduction audiogram are abnormal (a temporary conductive hearing loss is suspected), the audiologist may choose to defer speech perception testing until the ears are clear and hearing has improved. See Table 5.1 for a description of speech perception tests that are commonly used for the pediatric population and at which ages these tests should be performed when a child has normal speech and language development.

How Do Audiometric Masking Methods Differ in Children Compared with Adults?

The goal of a diagnostic hearing test is to determine the type, magnitude, and configuration of hearing loss for each ear. To accurately assess auditory function for each ear, proper masking techniques may be required. Masking allows the audiologist to isolate responses from the test ear (TE) by introducing noise to the non-test ear (NTE). This eliminates the possibility of the signal crossing over and eliciting a response from the NTE (Chapter 2).

The most common masking procedure is called the “plateau method.” “The masking plateau begins at the intensity at which the threshold in the TE remains stable when the masking noise in the NTE is increased.” ²⁴ It should be noted that there is not one universally accepted protocol for masking. Turner ²⁴ proposed that testing begin with an initial masking level of 10 dB above the air-conduction threshold of the NTE (i.e., 10 dB sensation level [SL]). The threshold of the TE is reestablished and masking noise (via narrow band noise stimulus) is increased another 10 dB. Once the masking plateau has been achieved, that is, when two consecutive 10 dB increases in masking is introduced without an observed shift in threshold of the TE, the response is documented on the audiogram. ²⁴

Other protocols call for an initial level of masking of 15 dB above the air-conduction threshold of the NTE (i.e., 15 dB SL) and three consecutive 5 dB increases for plateau to be reached. ²⁵ The same masking procedure is utilized for bone-conduction testing; however, correction factors of 20 dB at 250 Hz, 15 dB at 500 Hz, and 5 dB at 1,000 Hz need to be added to account for the occlusion effect if supra-aural headphones are used. A correction factor of 10 dB at 250 Hz is needed if insert earphones are being used. ²⁶

While the plateau method has been widely accepted as best practice for adult patients, pediatric audiologists often use a different approach. Masking can be very challenging and confusing for children. Some children have limited acceptance of the bone vibrator and retesting threshold multiple times while slowly increasing masking noise to the NTE to an effective level is not efficient. Instead of the plateau method, pediatric audiologists will often calculate the level of effective masking needed at the test frequency and present that level to the NTE. Once a response has been reliably obtained and repeated, the threshold of the TE and the masking level of the NTE will be recorded on the audiogram. By putting the effective masking level into the NTE when beginning testing, fewer responses are needed and more information can be obtained in one session. It is critical to determine effectively and efficiently the type of hearing loss so that medical management and treatment can be expedited.