ABR Summary and Review

Question 1

What can ABR be useful for?

Answer 1

Identifying space occupying lesions or retro-cochlear disease
Degenerative diseases (MS)
Auditory Neuropathy Diagnosis (ANSD)
Estimating Hearing Sensitivity

Question 2

Where do the waves arise from?

Answer 2

Wave I (AP) arises from the spiral ganglia and auditory nerve fibers exiting the cochlea
Wave II is thought to arrive from the central end of the VIIIth nerve
Waves III-V arise from multiple generators in the brainstem

Question 3

What are the two types of ABR exams?

Answer 3

Neurologic (rate) ABR - used to assess neural function with an emphasis on identifying intra-cranicular tumors or neurologic abnormalities
Threshold (hearing sensitivity) ABR - used to estimate hearing sensitivity and evaluate for ANSD

Question 4

Are rate study ABRs typically done with a click stimulus?

Answer 4

Yes, at a high intensity
80 dB nHL or greater

Question 5

Do you have to use masking much with rate ABR?

Answer 5

No
Unless there is a large asymmetry between ears

Question 6

What is an indication of ANSD?

Answer 6

If the cochlear microphonic continues past 2 ms at 90 and 80 dB nHL with no waves after
The resulting mirror image waveforms is the result of predominantly OHC excitation & inhibition known as the cochlear microphonic
OAEs are usually present but can disappear over time
ABR peaks are generally absent or abnormally delayed

Question 7

What is the ABR pattern for sensory hearing loss?

Answer 7

Wave I small, absent or slightly delayed
Interpeak latencies normal
Poor waveform morphology
Wave V can be delayed beyond normal

Question 8

What is the ABR pattern for conductive hearing loss?

Answer 8

Peak waveforms proportionally delayed
Normal (equal) interpeak latencies

Question 9

What is the ABR pattern for retrocochlear hearing loss?

Answer 9

Wave I normal typically (can be prolonged)
Interpeak latencies of I-III or III-V or both delayed
Absence of wave III and/or wave V
Replication difficult or absent

Question 10

Are ABRs good at detecting really small tumors (<1cm)?

Answer 10

No, only medium to large ones

Question 11

What is the standard protocol for estimating hearing thresholds?

Answer 11

Tympanometry and DPOAEs
Neurological Screening ABR (click ABR first, decrease in large steps for time and fill in prn)
Use condensation and rarefaction for initial high intensity run to rule out ANSD
Frequency specific ABR for threshold estimation (TB/Chirp) (begin at 30 to 40 dB SL re:AC click threshold)
Bone conduction (if needed)

Question 12

How do you determine if you need to mask for neurological ABR?

Answer 12

If the response is coming from the contralateral side, wave I will be prolonged
Normal wave I latency suggests that you don’t need to mask

Question 13

What suggests that there is not inter-aural symmetry of wave V absolute latency?

Answer 13

If they differ by more than 0.4 or 0.5 ms

Question 14

What is the correction factor for clicks?

Answer 14

10 dB nHL
or if you get a response at 30 dB or less, they are within normal limits

Question 15

Does an ABR threshold correlate with a audiometric threshold?

Answer 15

No, you need to apply a correction factor based on the stimuli that was presented

Question 16

What do you do if you cannot get a response at 80 dB nHL for a neurologic ABR?

Answer 16

Increase stimulus to 90 or 100 dB nHL
Then continue with tonebursts or narrow band chirps

Question 17

Does the use of insert earphones minimize the need for masking during AC ABR? What are the scenarios where you don’t need to mask?

Answer 17

Yes
Masking is not needed when the test intensity does not exceed the inter-aural attenuation for insert earphones (about 70 dB nHL)
Masking is not needed when the wave I is identified and occurs within the normal range
Masking is not needed when the latency of wave V is within normal limits for the stimulus intensity (if intensity >70 dB nHL and the only abnormality is delayed wave V, then contralateral ear should be masked)

Question 18

When would you use BC ABR?

Answer 18

To determine if hearing loss is conductive, sensory or mixed
Can be used for estimation of the air-bone gap (i.e., differences in your AC and BC responses is your air-bone gap for ABR)
Can be recorded on all ages

Question 19

Does BC ABR provide ear specific information without limitations of masking in the NTE?

Answer 19

Yes

Question 20

How does wave V differ for BC ABR than AC ABR?

Answer 20

Wave V is 0.5 ms shorter for BC than AC for intensities at equal sensation levels
Compare the lowest identifiable wave V latency to the same value for AC click stimuli

Question 21

Are bone conduction rates typically slower?

Answer 21

Yes
And they are done in alternating polarity to get rid of some of the noise in the response

Question 22

What is the interaural attenuation for BC for children and neonates?

Answer 22

IA for children is 15-25 dB
IA for neonates is 25-35 dB (bones not fully fused)

Question 23

Do different pathologies that cause lesions at the same level have similar effects on the ABR?

Answer 23

Yes, they might have the same pattern
It’s hard to determine what is actually going on until they go through surgery

Question 24

Does the tiptrode electrode work best when recording neurodiagnostic ABR on patient with HF SNHL?

Answer 24

Yes
The closer the electrode, the better the responses

Question 25

Were contralateral ABRs run more often in the past?

Answer 25

Yes, not as needed now with electrode switching

Question 26

What should you do if you have noisy recordings?

Answer 26

Tightly braid electrode leads (leads short as possible) Impedance equals 5 kohms or less Make sure amp cable not crossing over stimulus cable Amp at least 3 feet away from the base Increase number of averages Turn off “noise checking” (artifact reject – must increase # of averages to 8000) - a way to clean up the tracing; can be turned off if it is rejecting everything (last resort) Try another room and/or outlet Make sure patient is comfortable and breathing slowly out of mouth

Question 27

What should you do if you have impedance issues?

Answer 27

Prep small area where electrodes are to be placed vs forehead to nasion – help with electrodes and area acting as a large antenna Always check electrode leads for small breaks and adequate gel on pads You should have minimum 3cm distance between electrodes Infant skin is very thin and does not hold much fluid. Fluid is needed to conduct the electrical response. With high impedance and adequate prep you can try placing a saline soaked gauze pad over area or re-apply conductive gel to electrode Do not use fast rates for premature infants or with known neurological disease (61.1 rate for TB 2k/4k)(39.1 for 500/1k) - bc they have an immature system

Question 28

How to you have better wave V responses for tone bursts?

Answer 28

Better wave V for toneburst – record from nape of neck instead of ear (can record 2 channels with 2 montages to determine best resolution of wave V) Amp 1: A1 (-) to Fz (+) Amp 2: Az (-) nape of neck (-) to Fz (jumper cable)

Question 29

What is something to keep in mind if running an ABR in the OR?

Answer 29

Nitrous Oxide (sedation) creates positive middle ear pressure which may cause entire ABR to disappear, when NO goes away ABR will return to normal