Improved and more widespread screening programs identify more infants with hearing loss at an increasingly younger age. Helping families find and access appropriate early intervention services for their infants is a critical follow-up to these crucial evaluations.
Until the 1990s, children born with a significant hearing loss typically would not have been identified until 2 ½ to 3 years of age. But with the new universal programs that screen newborns for hearing loss, more children with congenital hearing loss are being identified at birth. Better coordinated and responsive follow-up systems also ensure earlier detection and treatment.
Auditory brainstem response (ABR) and otoacoustic emissions (OAE) screening techniques paved the way for quick, effective ways to screen the hearing of babies. The Rhode Island Hearing Assessment Project concluded that newborn hearing screening was both feasible and economically practical. Funded in 1989, the project was sponsored by the U.S. Health Resources Services Administration and the U.S. Office of Special Education and Rehabilitative Services.
In 1990, Hawaii was the first state to establish newborn hearing screening. Ten years later, 32 other states had passed newborn hearing screening legislation. All 50 states, the District of Columbia, and two territories now have Early Hearing Detection Intervention (EHDI) programs.
Healthy People 2000, a national health promotion and disease prevention initiative, sought an average age of 12 months for identification of congenital hearing loss. A decade later, Healthy People 2010 includes additional benchmarks: hearing screenings by one month, audiologic evaluation by three months, and early intervention by six months of age.
A Medical Home
For young children with congenital hearing loss, newborn hearing screening is the first step. The child's primary health care provider, in partnership with the parent(s), seeks to identify and meet the medical and non- medical needs of the child and family. This comprehensive approach, known as the "medical home," coordinates the audiologic evaluations and management, medical specialty evaluations, and early intervention services.
Follow-up services are crucial for babies whose initial screening indicates hearing loss. But many factors delay follow-up: families and primary care providers who do not confirm a newborn's hearing status after a failed screening; incomplete data or inadequate data systems for tracking and surveillance; and lack of appropriate services for infants identified with hearing loss, especially mild hearing loss.
Efforts to study and improve the rate of follow-up are underway in eight states through a learning collaborative of the National Initiative for Children's Healthcare Quality (NICHQ, www.nichq.org), a national organization dedicated to improving the quality of health care provided to children. NICHQ focuses on all components of the EHDI system (see sidebar) and identifies strategies to help move babies through the process in a timely manner.
However, one of the primary challenges for the EHDI system is the shortage of audiologists who are skilled in working with infants and very young children. As the EHDI system has grown, demand has increased for audiologists with the expertise to provide diagnostic, habilitation, counseling, and coordination services.
After identification of permanent hearing loss, referrals typically go to otolaryngology, genetics, ophthalmology, and early intervention services. Parents should be offered contacts for parent-to-parent support, an often-identified request of parents who have just discovered that their child has hearing loss.
If amplification is indicated for a baby with hearing loss, early, appropriate amplification requires accurate estimates of hearing sensitivity. For infants, a typical audiological test battery consists of ABR, high-frequency tympanometry, and OAEs, with behavioral audiometric testing when developmentally feasible. Data about threshold agreement between tone burst ABR and behavioral audiometric tests for children have been published, supporting the use of both tools.
Auditory steady-state response (ASSR) applications for infants and young children with hearing loss are continuing. However, some recent publications suggest that ASSR should be used cautiously with infants.
Delays to fitting amplification may be due to problems with scheduling, the need for repeat tests, suspicion of auditory neuropathy/dys-synchrony, and the cost of hearing aids (Harrison, et al, 2003). Delays in fittings also are likely for babies who are medically fragile or very premature.
The amplification process can be thought of as a five-step approach:
The selection stage begins the process of the infant's communication skill development. The family helps choose earmolds and hearing instruments; options are restricted by the relatively small size of infants' ears. The small sound bore limits earmold modifications that might otherwise enhance high-frequency amplification. The earmold material should be a soft material, typically silicone or vinyl.
Typically recommended pediatric hearing aids are binaural behind-the-ear and FM-compatible with flexible electroacoustic characteristics. Tamper-resistant features are necessary.
Acoustic feedback occurs often for babies, as they quickly outgrow earmolds. As a stopgap measure, lubricants can extend earmold use. Many hearing aids have feedback reduction circuitry—but verifying reduction is critical to assure uncompromised audibility.
Evidence for the specific circuitry to be used with infants is scant. Wide dynamic range compression (WDRC) hearing aids are appropriate for children who have mild to moderately severe hearing loss, according to a review of the literature by Palmer and Grimes (2005). They state that evidence supports the use of low compression thresholds, moderate compression ratios, and fast attack times.
A pediatric-specific prescriptive approach to ensure audibility of typical speech-level inputs guides electroacoustic targets for gain and output. The Desired Sensation Level (DSL) approach, developed by Seewald and colleagues, provides such targets. Three recent DSL articles in Trends in Amplification (2006) provide a historical perspective, as well as an update of the latest DSL version. These articles are a must-read for pediatric audiologists.
Verification, which can be behavioral or electroacoustic, focuses on whether speech audibility is met for a wide range of inputs audible. For infants, electroacoustic verification is the only feasible option. It provides frequency-specific information about the audibility for a wide variety of speech inputs, as well as estimates of the real-ear saturation response (RESR).
Because infants are unlikely to tolerate repeated probe-microphone measures, electroacoustic verification for them includes real-ear-to-coupler- difference (RECD) measures combined with coupler values to predict the real-ear aided response (REAR) and RESR. Predicted responses based on manufacturers' simulations of hearing instrument performance do not always predict real-ear performance.
To promote consistent hearing aid use, parents and/or caregivers need information about proper care, appearance, and benefits of the devices (Sjoblad, et al., 2001). Because every family is unique, it is important that the audiologist ask each parent about concerns at initial and follow-up sessions.
Demonstrations should include how to take care of the earmolds and hearing aids; insert the earmolds and put the hearing aids in place; and remove the devices. Practice and repetition are necessary, as with any new skill. Daily listening checks are vital because infants cannot tell anyone when a hearing aid is malfunctioning. The family must be supplied with hearing aid maintenance tools: batteries, earmold blower, drying system, listening tube/stethoscope, earmold lubricants, retention device, battery tester, and wax loops. All orientation information should be provided in written form.
Child-friendly retention devices, including pediatric tone hooks, help babies accept and retain the devices. Many manufacturers have pediatric hearing instrument care kits.
To validate the benefit of hearing aids, older children and adults complete speech perception measures while wearing the device. Babies require other validation measures, which often are subjective and depend on parent reports or clinician observations. Examples of subjective measures include the Early Listening Function (ELF), the Functional Auditory Performance Indicators (FAPI), and the Infant-Toddler Meaningful Auditory Integration (IT-MAIS).
The ultimate validation measure is speech and language development. In the early months of life, babbling and phoneme development should be monitored carefully. The partnership between parents, teachers, therapists, and audiologist is important to determine if changes in amplification are needed.
Following the identification and confirmation of hearing loss, and the hearing aid fitting, a reasonable follow-up schedule for children less than 2 years old is every three months. At that time hearing is monitored, hearing aids are tested and adjusted, and new earmolds are made when needed. Semiannual visits are appropriate for most children from 2 to 6 years of age, with annual follow-up thereafter, unless hearing-loss progression risk factors are present.