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Auditory brainstem response (ABR) Approximately 1 of every 1000 children is born deaf. Many more are born with less severe degrees of hearing impairment, while others may acquire hearing loss during early childhood. combination of technological advances in ABR and otoacoustic emissions (OAE) testing methods are used for evaluation of hearing in newborns.
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AUDITORY BRAINSTEM RESPONSE
(ABR)
Presented by
Dr. PANKAJ YADAV
NEWBORN HEARING SCREENING Approximately 1 of every 1000 children is
born deaf. Many more are born with less severe degrees of hearing impairment, while others may acquire hearing loss during early childhood.
combination of technological advances in ABR and otoacoustic emissions (OAE) testing methods are used for evaluation of hearing in newborns.
Automated auditory brainstem response (AABR) testing (eg, Algo-1 Plus) as an effective screening tool in the evaluation of hearing in newborns, with a sensitivity of 100% and specificity of 96-98%.
To screen for normal hearing, each ear may be evaluated independently, with a stimulus presented at an intensity level of 35-40 dB nHL.
Click-evoked ABR is highly correlated with hearing sensitivity in the frequency range from 1000-4000 Hz.
CRITERIA FOR SCREENING NEWBORN BABIES USING BERA 1. Parental concern about hearing levels
in their child 2. Family history of hearing loss 3. Pre and post natal infections 4. Low birth weight babies 5. Hyperbilirubinemia 6. Cranio facial deformities 7. Head injury 8. Persistent otitis media 9. Exposure to ototoxic drugs
INTRODUCTION
Auditory brainstem response (ABR) audiometry is a neurologic test of auditory brainstem function in response to auditory (click) stimuli.
Brain stem evoked response audiometry, Auditory brain stem response, ABR
audiometry, BAER (Brainstem auditory evoked response
audiometry). First described by Jewett and Williston in 1971
ABR audiometry refers to an evoked potential generated by a brief click or tone pip transmitted from an acoustic transducer in the form of an insert earphone or headphone. The elicited waveform response is measured by surface electrodes typically placed at the vertex of the scalp and ear lobes.
The amplitude (microvoltage) of the signal is averaged and charted against the time (millisecond), much like an EEG.
The waveform peaks are labeled I-VII. These waveforms normally occur within a 10-
millisecond time period after a click stimulus presented at high intensities (70-90 dB normal hearing level [nHL]).
PROCEDURE Electrode Placement: Disposable electrodes are placed using the
following guideline for “Dual Channel System Configuration”: Red, Side A: Right Mastoids Red, Side B: Left Mastoid Black: Forehead below blue Blue: Forehead above black
Impedance Testing: Before performing ABR testing, electrode impedances were
checked. Checking for Electrical Noise:
Before beginning the test, it was checked to make sure the EEG activity, in the EEG and Amplifier window, was normal for a relaxed state and that the signal did not contain artifacts waveforms reflecting electrical noise.
ABR TESTING PROCEDURE CONTD. The following settings are used:
Stimulus: 0.1 milliseconds Broadband Click Rate: 29.3/sec Polarity: Rarefaction Transducers: Insert Earphones Intensity: 90 dB HL down to 30 dB HL for threshold
detection (wave V) Filters: 100 – 3000 Hz Notch Filter: ON Amplification: 100x Runs: 2-4 Analysis Time Window: 12.8 milliseconds Sweeps: 2048 Electrode Montage: contra-lateral Array
ABR TESTING PROCEDURE CONTD. Recording of ABR:
The recordings were started from 70 dB intensity and than successively increased or decreased as per identification of wave V peak.
Wave V was traced at successively lower intensities to find out minimum intensity at which it is elicited known as “Hearing Threshold”.
Both ipsi-lateral and contra-lateral recordings were made for each ear.
Multiple recordings were carried out at each intensity and were superimposed, to check the reproducibility of the waves thus obtained.
The median time taken for ABR 25 min including 10 min of patient preparation.
WAVEFORM COMPONENTS
Wave I - The ABR wave I response is the representation of the compound auditory nerve action potential in the distal portion of cranial nerve (CN) VIII from afferent activity of the CN VIII fibers (first-order neurons) as they leave the cochlea and enter the internal auditory canal.
Wave II - The ABR wave II is generated by the proximal VIII nerve as it enters the brain stem.
Wave III: The ABR wave III arises from second-order neuron activity (beyond CN VIII) in or near the cochlear nucleus in the caudal portion of the auditory pons.
Wave IV: The ABR wave IV, which often shares the same peak with wave V, arise from pontine third-order neurons mostly located in the superior olivary complex, but additional contributions may come from the cochlear nucleus and nucleus of lateral lemniscus.
Wave V: reflects activity of multiple anatomic auditory structures. The ABR wave V is the component analyzed most often in clinical applications of the ABR. Although some debate exists regarding the precise generation of wave V, it is believed to originate from the vicinity of the inferior colliculus. The second-order neuron activity may additionally contribute in some way to wave V.
Wave VI and VII: Thalamic (medial geniculate body) and cortical region.
BERA FINDINGS SUGGESTIVE OF RETROCOCHLEAR PATHOLOGY
1. Absolute latency interaural difference wave V (IT5) - Prolonged
2. I-V interpeak interval interaural difference - Prolonged
3. Absolute latency of wave V - Prolonged as compared with normative data
4. Absolute latencies and interpeak intervals latencies I-III, I-V, III-V - Prolonged as compared with normative data
5. Absent auditory brainstem response in the involved ear
USES OF BERA 1. It is an effective screening tool for
evaluating cases of deafness due to retrocochlear pathology i.e. (Acoustic schwannoma).
2. Used in screening newborns for deafness
3. Used for intraoperative monitoring of central and peripheral nervous system
4. Monitoting patients in intensive care units
5. Diagnosing suspected demyelination disorders
LIMITATION1. 1. All waves are absent in severe hearing
loss as well as in a large acoustic neuroma.2. 2. A normal BERA response virtually rules out
an acoustic neuroma; but doesn’t at all rule out intrinsic brainstem lesion or even non-acoustic tumor of the CP angle e.g. Meningioma.
