CHAPTER and systematic neonatal hearing screening is the

CHAPTER – 1

INTRODUCTION

 

Hearing plays a significant role in
language and intellectual development. The impact of early diagnosis and
rehabilitation of newborns with hearing loss cannot be overstated. Since the
disease develops gradually over years while first signs can be detected early;
therefore early screening is the best way of prevention of advanced hearing
disorders. Congenital and acquired hearing loss in newborns and children can
lead to deficiencies and defects in the evolution of speech, poor educational
function, and lifelong social non-concurrence and emotional distress.
Pediatricians are required to identify at-risk children, intervene in a timely
and effective manner, and refer patients as necessary.The importance of early
diagnosis is cle ar, but diagnosis and treatment in the 1st months of life is a recent concept.The
initial signs of hearing loss are very subtle and systematic neonatal hearing
screening is the most effective tool for early detection of it. Hearing loss
affects around 3 out of every 1000 live births

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Hearing is essential for
speech and language development, communication and learning. Children with
hearing loss continue to be under identified and underserved population and
their life is affected both quantitatively and qualitatively. Hearing loss in
children constitutes a considerable handicap because it is an invisible
disability that can compromise their optimal development and personal
achievement. The prevalence of congenital hearing loss has  been estimated to be 1.2  – 5.7 per thousand live births Early
detection and appropriate treatment provides 
the best choice maximizing the critical period of hearing and  thereby availing the resources to improve
hearing and oral  communication skills.
On the other hand late detection and treatment leaves the children with poor
speech development and school achievement. Programmes that focus on detecting
hearing disabilities at an early part of life help in improving the overall
development of the child in cognitive, motor and social domain.

The incidence of sensorineural
hearing loss is approximately 1-3/1,000 newborns.This is 1/1,000 about severe
to deep deafness (70 db or greater). Therefore, only 2-5% of newborns has
deafness or hearing loss and the remaining (95-98%) are normal.50% of children
with a severe to profound congenital hearing loss have no risk factors for
deafness. This means that screening of at-risk children only misses 50% of
congenital hearing loss. For this reason, screening of all newborns has been
recommended.

Both the auditory brainstem
response (ABR) and the otoacoustic emission (OAE) test are used to screen
hearing in newborns. The OAE test measures the response of the cochlea to noise
emitted by a microphone in the external ear canal and reflects the status of
the peripheral auditory system and the outer hair cells. The ABR test uses a
surface electrode to measure neural activity in the cochlea, auditory nerve and
brainstem in response to acoustic stimuli, reflecting the status of the
peripheral auditory system, the eighth nerve and the auditory brainstem.

Recommended Protocol for Infant Audiologic
Assessment

The following protocol was developed to
facilitate the diagnosis
of hearing loss, medical clearance for amplification, and use of
amplification for infants with hearing loss by three months of age. An
audiologist should have the necessary equipment (ABR with bone conduction and
tone bursts, OAE, high frequency tympanometry) and be experienced in the
assessment of infants. Infants should obtain a diagnostic assessment after a
failed/referred (that is, an abnormal) newborn hearing screen. A hearing screen
is considered failed when one or both ears do not pass the hospital screen or
outpatient re-screen. Within the first two months of life, the procedures
outlined below in Step I and Step II, should be completed on all infants
referred from the screening process. Use the Newborn Audiological Assessment
Checklist found in Appendix 1 to assure that all recommended follow-up
activities have been completed. The activities outlined in Step III, for
children with confirmed hearing loss, should occur by three months of age.For
infants who pass both ABR and OAEs (robust responses at 3 or more frequencies),
parents should receive information about hearing, speech, and language
milestones and information regarding risk indicators for progressive hearing
loss. Parents should be instructed that, if questions about their child’s
hearing or speech and language development arise at any point, their child
should receive an age-appropriate audiologic assessment.

For infants who pass both ABR and OAEs (robust responses
at 3 or more frequencies), parents should receive information about
hearing, speech, and language milestones and information regarding risk
indicators for
progressive hearing loss. Parents should be instructed that, if
questions about
their child’s hearing or speech and language development arise at any point,
their child should receive an age-appropriate audiologic assessment.

Infants who pass ABR but who do not pass OAEs
may have external and/or middle ear pathology and should be referred to a
physician experienced in evaluating external and middle ear function in
infants. A repeat audiologic assessment should be completed after this
evaluation. The assessment should occur by three months of age and should
include repeat OAEs.

 

Infants who pass OAEs but who do not pass ABR
should continue with the recommended assessments outlined in Step II below.
Infants who fail both OAEs and ABR in one or both ears should continue with the
recommended assessments as outlined in Step II.

Definition of
Threshold In the
NHSP AC click ABR protocol4 the definition of ABR threshold is “the lowest level at
which a clear response is present, with the absence of a recordable response
at a level 5 or 10dB below the threshold, obtained under good recording conditions.
The provisional NHSP definition for the ASSR threshold, for each frequency
tested, is the equivalent to this, i.e. the lowest level at which the target response
at a level 5 or 10dB below this threshold, obtained under good recording conditions
(defined as p >0.02 with the noise floor <10nV). There should also be a response meeting the p<0.02 criteria at 5 or 10dB above threshold. If threshold is at the maximum stimulus level there should be a further run at the maximum stimulus level meeting the p<0.02 criteria instead of the run at 5 or 10dB above threshold. response criteria value of p<0.02 is obtained, with the absence of a recordable.   Otoacoustic emissions (OAEs) are low-intensity sounds emitted by functioning outer hair cells of the cochlea. OAEs are measured by acoustic stimuli such as a series of very brief clicks to the ear through a probe that is inserted in the outer third of the ear canal. The probe contains loudspeakers that generate the clicks and a microphone for measuring the resulting OAEs. OAE testing requires no behavioral or interactive feedback by the individual being tested. OAEs are used as a screening test for hearing in newborns. Other potential applications of OAE testing include screening children or at-risk populations for hearing loss, and characterizing sensitivity and functional hearing loss and differentiating sensory from neural components in people with known hearing loss. OAE devices use either transient evoked OAE (TEOAE) or distortion product EOE (DPOAE) technology. TEOAE devices emit a single brief click that covers a broad frequency range. DPOAE devices emit two brief tones set at two separate frequencies. TEOAEs are used to screen infants, validate other tests, and assess cochlear function, and DPOAEs are used to assess cochlear damage, ototoxicity, and noise-induced damage. Spontaneous otoacoustic emissions (SOAEs) are sounds emitted without an acoustic stimulus (i.e., spontaneously). Stimulus-frequency otoacoustic emissions (SFOAEs) are sounds emitted in response to a continuous tone. At present, SOAEs and SFOAEs are not used clinically. There is inadequate evidence that hearing screening with OAEs is superior to screening audiometry in improving health outcomes such as timely facilitation of speech, language, and communication skills in older children or adults.     Otoacoustic emissions (OAEs) testing as a diagnostic service is medically necessary for the evaluation of hearing loss in one or more of the following: Infants over 90 days old and children up to 4 years of age,  children and adults who are or who are unable to cooperate with other methods of hearing testing (e.g. individuals with autism or stroke),  children with developmental or delayed speech or language disorders, individuals with tinnitus, acoustic trauma, noise induced hearing loss, or sudden hearing loss, individuals with abnormal auditory perception,  individuals with sensorineural hearing loss,  individuals with abnormal auditory function studies or failed hearing exam, potentially malingering individuals who may be feigning a hearing loss,  monitoring of ototoxicity in patients before, during, and after administration of agents known to be ototoxic (e.g., aminoglycosides, chemotherapy agents)   A study which involved 53,781 newborns provided a direct comparison of hearing impairment detection rates during periods of newborn hearing screening and no screening in the same hospitals (Wessex Universal Hearing Screening Trial, 1998). Those infants born during a period of screening underwent a two-stage screening test, with transient evoked otoacoustic emissions (TEOAE) at birth, followed by automated auditory brainstem response (AABR) before discharge if the first screen was failed. If the second screen was also failed, the babies were referred to an audiologist at 6 to 12 weeks of age. In this study, 4% of infants with hearing loss were missed during the screening period, while 27% were missed during the period of no screening. This study did not provide data on clinical outcomes such as speech and language development in screened versus unscreened children.   Another group of investigators compared clinical outcomes, including speech and language development, in 25 infants who were screened as part of the Colorado Universal Newborn Screening program with outcomes in 25 matched infants who were born in a hospital without a universal newborn hearing screening program (Yoshinaga-Itano et al., 2000). This study found that children who were identified as hearing impaired through the newborn hearing screening program had significantly better scores on tests of speech and language development than did children who were identified later. There are many behavioral and electrophysiological assessment methods for screening of hearing in neonates. Behavioral techniques have a high number of false negative results. As electrophysiologic methods with greater sensitivity and specificity, the following may be used: auditory brainstem response (ABR) automated auditory brainstem response (AABR) and evoked oto-acoustic emissions (EOAE). ABR and OAE are used for universal hearing screening. However, it is better to minimize false-positive results in developing a more reliable newborn hearing screening program. OAE and ABR tools are evolving and becoming more and more automated. Determining which of them is most effective is interesting. ABR is a standard and very precise test in determining the average threshold of frequencies at 2000-4000 Hz. The differences in the size of the external auditory canal and in the placement and type of earphone can produce small differences in the stimulus and therefore can lead to false negative results in mild hearing losses. False positive results of it seem to be fewer. OAE tests are generally thought to be easier to administer and faster. The time needed for screening test is variable. However, the average time to carry out automated ABR testing ranges from 8 to 15 min, and conventional OAE tests take 2 to 13 min This measures not only the integrity of the inner ear, but also the auditory pathway. It can therefore detect the rare condition of auditory neuropathy, in children who are deaf but have normal OAE's (because the cochlea is normal). The stimulus (either clicks or tones) is presented using either earphones or an ear canal probe, and the electrophysiological response from the brainstem is detected by scalp electrodes. Automated devices allow screening to be performed by non-specialists. Responses from a large number of stimulus presentations are averaged and the automated screener uses a response algorithm to produce a 'pass' or 'refer' result. The "pass" level is set at about 35 decibels. This test takes 15-20 min, but once again this time may be longer if a child is restless, and does not include time for discussion and preparation before the test. DPOAE test performance was compromised at 1.1 kHz. In view of the different test performance characteristics across the frequencies, the use of a fixed SNR as a pass criterion for all frequencies in DPOAE assessments is not recommended. When compared to pure tone plus tympanometry results, the DPOAEs showed deterioration in test performance, suggesting that the use of DPOAEs alone might miss children with subtle middle ear dysfunction. However, when the results of a test protocol, which incorporates both DPOAEs and tympanometry, were used in comparison with the gold standard of pure-tone screening plus tympanometry, test performance was enhanced. The investigators concluded that In view of its high performance, the use of a protocol that includes both DPOAEs and tympanometry holds promise as a useful tool in the hearing screening of schoolchildren, including difficult-to-test children. Early diagnosis and immediate intervention play important role in the development and prognosis of children with hearing loss and decrease the impact of the condition on the child's social, emotional, intellectual and linguistic development   This study addressed the following question with respect to neonatal screening:  To evaluate out the efficacy of  Auditory Brainstem Response (ABR), Distortion Product Otoacoustic Emission (DPOAE) and Auditory Steady State Response, in screening the hearing loss  in Indian population, and to know among all  above test is more specific and sensitive  in screening the hearing loss  in Indian population. This can help to better diagnosis and better prognosis.   Purpose of study: The main purpose of this study is to This st addressed the following question with respect to neonatal screening:  To evaluate the efficacy of  auditory Brainstem Response (ABR), Distortion Product Otoacoustic Emission (DPOAE) and Auditory Steady State Response, in screening the hearing loss  in Indian population, and to know among all  above test is more specific and sensitive  in screening the hearing loss  in Indian population. Also to compare the result between demographic variable such as  Type of delivery, Birth weight, APGAR Score, Family history, Age of the Mother, Hypertension, Diabetes and Delivery  This can help to better diagnosis and better prognosis. Implication of the Study: Early diagnosis and acute intervention plays an  important role in the development and prognosis of children with hearing loss and decrease the impact of the condition on the child's social, emotional, intellectual and linguistic development. Better form of screening will give exact level of hearing loss and pathology that will help for early diagnosis and better treatment. This study helped to know better form of neonatal screening which can help to early diagnosis and early interventions.  

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