Atlas of Procedures in Neonatology, 4th Edition
Neonatal Hearing Screening
Rachel St. John
Susan H. Morgan
- Otoacoustic emissions (OAE): A screening tool that measures sounds generated by a functioning cochlea. A probe containing a microphone delivers a sound stimulus into the ear and records the response that travels back out of the cochlea, through the middle ear, and into the ear canal.
- Automated auditory brainstem response (AABR): A screening tool that records auditory brainstem responses and compares them to a template representing typical results in neonates. Click sounds are delivered by earphones into the ear canal, and electrodes placed on the head and nape of neck register the auditory brainstem response. In addition to assessing middle ear and cochlear activity, this test evaluates the function of the auditory nerve and auditory brainstem.
- Auditory brainstem responses (ABR); may also be referred to as brainstem auditory evoked response (BAER): A diagnostic test used to predict type and severity of hearing loss. ABR testing is conducted after a failed screening measurement. Auditory brainstem responses are determined in each ear for both click and tone stimuli. These sounds are presented by air (earphone) as well as bone conduction. Severity of hearing loss is expressed in decibels and described as conductive, sensorineural, or mixed.
- Identifying and providing early intervention for children with congenital hearing loss to minimize delay in speech and language development.
- Supporting accurate reporting by state of incidence of congenital hearing loss.
- The incidence of congenital hearing loss in the general population is approximately 2 to 4 in 1,000 live births in the United States (1).
- The risk for hearing loss can increase substantially when infants are exposed to known perinatal risk factors for hearing loss, such as TORCH infections, significant hyperbilirubinemia, and ototoxic medications. As technology improves and the number of at-risk infants graduating from neonatal intensive care nurseries rises (2), the need for early identification of hearing loss and intervention becomes even more critical.
- Any infant who fails hearing screening needs to be immediately referred to a pediatric audiologist. Delaying diagnosis of hearing loss can lead to significant problems in language and speech acquisition. The Centers for Disease Control Early Hearing Detection and Intervention Program recommends that infants identified by a failed hearing screen be referred for a comprehensive audiology evaluation as soon as possible, and always before 3 months of age.
- Ideally, every newborn should receive a hearing screen before discharge from the hospital.In 1993, the National Institutes of Health (NIH) Consensus on Early Identification of Hearing Loss concluded that all infants should be screened for hearing impairment prior to hospital discharge, if possible (3). The American Academy of Pediatrics officially endorsed these recommendations in 1999.
Over the past 13 years, widespread support has led to state-mandated or state volunteer programs throughout the United States. Currently, 39 states and the District of Columbia have passed legislation mandating universal newborn hearing screening—that is, hearing screening for every infant, regardless of background and risk factors (4).
- Infants who meet high-risk criteria for acquiring hearing loss warrant immediate hearing screening, as well as ongoing monitoring. Table 51.1 lists factors known to contribute to neonatal hearing loss (5). It is critical that infants with any of these risk factors be referred to audiology after discharge, even if they have passed their
initial hearing screen, in order that they may continue to be monitored during the years of initial language acquisition and development.
TABLE 51.1 High-Risk Registry to Screen Selectively for Hearing Loss
· Illness or condition that requires admission of 48 hours or longer to neonatal intensive care unit
· Stigmata or other findings associated with a syndrome known to include sensorineural or conductive hearing loss
· Family history of permanent childhood sensorineural hearing loss
· Craniofacial anomalies, including those with morphologic abnormalities of the pinna and ear canal
· In utero infection, such as cytomegalovirus, herpes, toxoplasmosis, or rubella
· Parental or caregiver concern regarding hearing, speech, language, and developmental delay
· Postnatal infections associated with sensorineural hearing loss, including bacterial meningitis
· Neonatal indicators, specifically hyperbilirubinemia at a serum level that requires exchange transfusion, persistent pulmonary hypertension of the newborn associated with mechanical ventilation, and conditions that require the use of extracorporeal membrane oxygenation
· Syndromes associated with progressive hearing loss, such as neurofibromatosis, osteopetrosis, and Usher syndrome
· Neurodegenerative disorders, such as Hunter syndrome, or sensory motor neuropathies, such as Friedreich ataxia and Charcot-Marie-Tooth syndrome
· Head trauma
· Recurrent or persistent otitis media with effusion for at least 3 months
- Patient has significantly atretic or total lack of external ear canal: Refer directly to pediatric audiologist.
- Although it is certainly fair to rescreen an infant who has potentially failed screening because of excessive background noise, vernix in ear canal, etc., multiple rescreening attempts in hopes of eventually obtaining a “pass” are not recommended and can contribute to delayed identification of congenital hearing loss.
- Infant hearing screening can be compromised by environmental noise (such as a busy intensive care unit) or infant movement. OAE screening, more so than AABR, is particularly affected by vernix occluding the ear canal, or middle ear pathology such as effusion (6).
- OAE screening, although less time-consuming to set up and conduct, has a higher “refer” (fail) rate than AABR. The refer rates for OAE screening alone have been cited in the literature as being between 5.8% and 6.5%, with refer rates using AABR screening around 3.2% (7,8). In particular, infants who are <48 hours old are more likely to have a “refer” result if screened with OAE, as the presence of vernix and debris in the ear canal can be a significant factor (9). There is no standardization of newborn hearing screening protocols in the United States at this time, and both technologies are in wide use.
- It is difficult to state accurately how many infants who “fail” their hearing screen actually do hear normally (have a “false-positive” result). This is due mainly to the fact that, for a variety of reasons, a significant number of patients who get a “refer” result do not follow up for diagnosis with an audiologist. The Joint Committee on Infant Hearing benchmark for diagnostic follow-up is 70%, and there are large programs that have shown steady improvement toward meeting or exceeding this standard (10,11). In sparsely populated areas of the country, where resources are limited, however, as many as 90% of infants requiring diagnostic assessment are lost to follow-up (12). Similarly, the number of infants who pass their hearing screen and ultimately end up with a diagnosis of hearing loss (“false-negative” result) is difficult to assess. Children whose hearing loss is not present at birth but develops later on (“late-onset” or “acquired” hearing loss) truly do pass their newborn hearing screenings. They are not “missed” by screening: Their hearing loss is different in nature than hearing loss that is present at birth (13).
- An OAE screening system consists of a miniature microphone housed in a probe that emits either click or tone stimuli. This assembly is coupled to a computer for analysis of the sound in the ear canal and processing of the otoacoustic emission. Results may be automatically analyzed and interpreted as either “pass” or “refer” for each ear. Figure 51.1 shows an infant undergoing OAE screening.
- An AABR screening system consists of occlusive earphones that cover the ears and emit sound stimuli.
Electrodes placed on the head and the back of the neck detect electrical activity from the auditory nerve and brainstem. A computer registers samples of the electrical activity over a fixed period of time. The averaged responses are then compared to a normal newborn template to determine if the result is a “pass” or a “refer” for each ear. Figure 51.2 shows an infant undergoing AABR screening.
FIG. 51.1. An infant undergoing OAE screening.
Care should be taken to attempt screening in a relatively quiet environment, as well as ensuring that the infant is resting comfortably and the ear canals are free from obvious debris.
FIG. 51.2. An infant undergoing AABR screening.
- Special Circumstances
- Hearing parents whose infant does not pass a hearing screening:Parents are often quite concerned to learn that their infant has not passed a hearing screening. This can be especially stress-provoking for parents whose infant may have spent a good deal of time in a neonatal intensive care unit (NICU) and may be facing additional medical concerns upon discharge. It is extremely important to remember that a failed hearing screening is not a definitive diagnosis of hearing loss.It is an important indicator that the infant needs immediate referral to an audiologist for further detailed evaluation, which may or may not result in a formal diagnosis of hearing loss.
- Deaf parents whose infant does not pass a hearing screen:Deaf parents, especially culturally Deaf individuals who use American Sign Language and identify strongly with being members of the Deaf community, are often thrilled to find out that their infant may have hearing loss. This is a cultural identification: These parents are rejoicing in the fact that their infant is like them and will have a cultural place of significance in their social world. This is often in direct opposition to the traditional medical perspective on hearing loss (as a pathology that needs to be addressed and “fixed”), and the parental reaction can be frankly shocking for involved health care professionals. It is very important to realize that these infants of culturally Deaf parents are not facing the immediate crisis of delayed language development referred to earlier. American Sign Language is a well-researched, intact language (14,15) that is immediately accessible to an infant of Deaf parents. Although it is still extremely important to establish audiologic follow-up for these infants of Deaf parents who fail a hearing screen, it is also critical to respect the potential cultural implication for such families. These parents may be celebrating in a manner very similar to hearing parents who are happy that their infant has passed the hearing screening.
Both OAE and AABR screening systems can be automated: An individual only needs to be appropriately trained to set up and apply the equipment. A computer processes the incoming information and gives a readout of the result, usually as “pass” or “refer.”
OAE and AABR are considered to be noninvasive and safe procedures. Like any procedure that involves the application of electrode pads, mild superficial skin abrasions could possibly occur with the removal of the electrode pads after AABR testing (16).
- Centers for Disease Control.Early Hearing Detection and Intervention Program. Available at: www.cdc.gov/ncbddd/ehdi/FAQ/questionsgeneralHL.htm#prev. Accessed January 21, 2006.
- Kessenich M.Developmental outcomes of premature, low birth weight, and medically fragile infants. NBIN. 2003;3(3): 80–87.
- Early Identification of Hearing Impairment in Infants and Young Children.NIH Consens Statement Online 1993 Mar 1–3 [cited January 21, 2006];11(1):1–24.
- Status of State Universal Newborn and Infant Hearing Screening Legislation and Laws.Available at: www.asha.org/about/legislation-advocacy/state/issues/overview.htm. Accessed January 21, 2006.
- Joint Committee on Infant Hearing.Year 2000 Position Statement: principles and guidelines for early hearing detection and intervention programs. Pediatrics. 2000;106:798–817.
- De Michele A.Newborn hearing screening. eMedicine. 2005. Available at: www.emedicine.com/ent/topic576.htm. Accessed February 13, 2006.
- Vohr B, Oh W, Stewart E, et al. Comparison of costs and referral rates of 3 universal newborn hearing screening protocols. J Pediatr.2001;139(2):238–244.
- Clarke P, Iqbal M, Mitchell S.A comparison of transient-evoked otoacoustic emissions and automated auditory brainstem responses for pre-discharge neonatal hearing screening. Int J Audiol. 2003;42(8):443–447.
- Lin H, Shu M, Lee K, et al. Comparison of hearing screening programs between one step with transient evoked otoacoustic emissions (TEOAE) and two steps with TEOAE and automated auditory brainstem response (AABR). Laryngoscope.2005;115
- Prieve B, Dalzell L, Berg A, et al. The New York State Universal Newborn Hearing Screening Demonstration Project: outpatient outcome measures. Ear Hearing. 2000;21:104–117.
- Vohr BR, Carty LM, Moore PE, Letourneau K.The Rhode Island Hearing Assessment Program: experience with statewide hearing screening (1993–1996). J Pediatr. 1998:133(3):353–357.
- Estimated Number of Infants Receiving Diagnostic Evaluation(2004). Available at: www.cdc.gov/ncbddd/ehdi/2004/Eval_04_A_web.pdf. Accessed July 21, 2006.
- Weichbold V, Nekahm-Heis D, Welzl-Mueller K.Ten year outcome of newborn hearing screening in Austria. Int J Pediatr Otorhinolaryngol. 2006;70:235–240.
- Stokoe W.A Dictionary of American Sign Language on Linguistic Principles. Washington, DC: Gallaudet Press; 1965, rev. ed. 1976.
- Stokoe W.Sign language structure. Annu Rev Anthropol. 1980;9:365–390.
- National Library of Medicine, Health Services/Technology Assessment Text. Health Technology Advisory Committee—Minnesota (Static collection) page. Available at: www.ncbi.nlm. nih.gov/books/bv.fcgi?rid=hstat6.section.3839. Accessed January 21, 2006.