Page 2148 - Cote clinical veterinary advisor dogs and cats 4th

Brainstem Auditory Evoked Response (BAER) Test 1070.e3

• Otoscopic examination: to ensure that to ensure there is not a technical problem and do initial screening, but this level has been
ear canal is open and free from significant to prevent incorrectly diagnosing deafness. determined to be comfortable for the animal
VetBooks.ir occluded ear canal will not transmit sound to Procedure • Set signal averager to average 1000 signals
and effective for identifying potential hearing
amounts of debris or exudate. A stenotic or
deficits.
the tympanum and will result in subnormal
• Place animal in sternal recumbency or in a
sitting position.
waveform amplitudes and prolonged wave I
latency. Ear canals may need to be cleaned • Turn on computer, load appropriate software (256 may be adequate for cats or uncoopera-
tive dogs if the waveform is clearly normal),
before the BAER test. Clinicians should and protocols, and set up animal record. and select right or left ear to begin recording.
visually assess the integrity of the tympanic • Perform an otoscopic examination, and clean • Each ear should be recorded twice, and the
membrane. ears if necessary. recorded waveforms should be compared.
• Ensure that right and left ear electrodes are • Insert subdermal electrodes. They should be very similar. If not, do a
appropriately placed and noted correctly on ○ Reference: mastoid. Place electrode subcu- technical check, and repeat the test.
the computer. taneously, adjacent to where the horizontal • Once good-quality recordings have been
ear canal begins just rostral to the base of recorded for both ears, the waveforms should
Possible Complications and the ear (usually at the caudal end of the be labeled and amplitudes and latencies
Common Errors to Avoid zygomatic arch). The T1 reference may calculated. Procedures and Techniques
• Ear canals filled with exudate, cerumen, or also be used just dorsal to the spinous • Subdermal electrodes and inserted micro-
debris process of T1. phones are then removed, and the animal
• Testing puppies that are too young; puppies ○ Recording electrode: vertex. Place the can be discharged.
should be at least 6 weeks of age when tested. electrode midline, halfway between the
• Although general anesthesia has little effect occipital crest and orbits. Postprocedure
on the BAER test, hypothermia will prolong ○ Ground electrode: place the electrode If the animal has been sedated, allow it to
latencies. midline over the second to fourth cervical recover sufficiently before discharge.
• Inserted microphones not placed sufficiently vertebrae.
deeply in the ear canal or positioned such • Check electrode impedance (usually in the Alternatives and Their
that the sound is directed into the wall of computer software) to ensure that electrodes Relative Merits
the ear canal instead of down the lumen are working appropriately. There are no practical and accurate alternatives
• Subdermal electrodes become dislodged. • Place foam insert microphones in right to establishing unilateral or bilateral deafness
• If flatline or grossly abnormal recording is and left ear canals; place them so they are in dogs and cats. Bilateral deafness can usually
obtained, always do a thorough technical well seated in the upper (distal) third of be suspected but not confirmed by subjective
check (e.g., computer working, sound is the vertical ear canal. If using headphones, assessment of the animal’s response to loud
generated in the microphones, subdermal ensure that the pinnae are not obstructing noises.
electrodes in place and not dislodged, the headphones and a snug seal is established
inserted microphones placed appropriately over the ear canal. AUTHOR: Greg Kilburn, DVM, DACVIM
EDITORS: Leah A. Cohn, DVM, PhD, DACVIM; Mark S.
in the ear canal) to ensure that the result is • Set sound intensity at 80 dB. There is no Thompson, DVM, DABVP
real. A known normal dog can be evaluated established appropriate sound intensity to

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