CHAPTER and systematic neonatal hearing screening is the

CHAPTER – 1

INTRODUCTION

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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

.

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

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