Summary of Two channel bone conduction ABR testing: An interview with Inga Ferm

Summary of Main Ideas and Concepts

Two-Channel Bone Conduction ABR Testing is a diagnostic method used to record Auditory Brainstem Responses (ABR) from both the ipsilateral (same side) and contralateral (opposite side) ears simultaneously during bone conduction stimulation. This approach helps clarify which ear is generating the response, especially in complex clinical situations.

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Key Points and Lessons

• Purpose of Two-Channel Bone Conduction Testing:
  • Records responses from both ipsilateral and contralateral sides simultaneously.
  • Helps determine if the recorded response is truly from the stimulated ear or a cross-hearing response.
  • Used primarily when:
    • There is an air-bone gap greater than 5 dB HL.
    • Masking decisions need to be considered.
    • Bilateral conductive hearing loss is present (e.g., bilateral glue ear or bilateral atresias).
    • Babies or young children cannot tolerate two transducers simultaneously.
• Electrode and Equipment Setup:
  • Four electrodes are used:
    • Positive Electrode on the high forehead (instead of vertex, especially in babies).
    • Negative electrodes behind each ear on the lower mastoid.
    • Common (ground) Electrode placed about 4 cm away from the high forehead, often on the right eyebrow.
  • Bone Conductor placed behind the ear of interest, avoiding Electrode wires and preamp box cables.
  • Testing proceeds as normal once setup is complete.
• Interpreting Two-Channel ABR Results:
  • Use software (e.g., Eclipse) to view two-channel responses.
  • Compare ipsilateral and contralateral waveforms:
    • Larger and earlier wave V amplitude on ipsilateral side indicates response is from the stimulated ear.
    • Larger or earlier contralateral response suggests cross-hearing; masking may be necessary.
  • Latency shifts and amplitude differences are key indicators.
  • Example overlays can help visualize amplitude and latency differences between ipsilateral and contralateral responses.
• Benefits of Two-Channel Testing:
  • Provides ear-specific information quickly and straightforwardly.
  • Can reduce the need for masking, saving time.
  • Useful in bilateral conductive losses where masking levels might be problematic.
  • Helpful when infants do not tolerate air conduction transducers alongside bone conductors.
• Limitations and Recommendations:
  • Recommended primarily for babies and children under 2 years old.
  • In older children and adults, contralateral responses can be larger and earlier, causing confusion.
  • Bone conduction testing is contraindicated in patients with certain medical devices (e.g., digital VP Shunts).
  • Interpretation can be challenging due to variable waveform morphology.
  • Testing must be done on both ears; contralateral data cannot replace direct testing.
  • Focus on wave V to SN10 amplitude for reliable interpretation rather than wave III, which may be larger or earlier on contralateral side unpredictably.

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Methodology / Instructions for Two-Channel Bone Conduction ABR Testing

1. Electrode Placement:
   • Place positive Electrode on the high forehead.
   • Place negative electrodes on the lower mastoid behind each ear.
   • Place common (ground) Electrode about 4 cm from the high forehead, e.g., right eyebrow.
2. Bone Conductor Placement:
   • Position Bone Conductor behind the ear of interest.
   • Avoid interference with Electrode wires and preamp cables.
   • Secure Bone Conductor firmly.
3. Equipment Setup:
   • Use an ABR system capable of two-channel recording (e.g., Eclipse).
   • Select the two-channel mode via the software toolbar once electrodes are connected.
4. Testing Procedure:
   • Stimulate via bone conduction.
   • Record simultaneous ipsilateral and contralateral responses.
   • Observe wave V amplitude and latency on both channels.
5. Interpretation:
   • Confirm larger and earlier wave V on ipsilateral side to attribute response to stimulated ear.
   • If contralateral response is larger or earlier, consider masking to avoid cross-hearing.
   • Use overlays to compare waveforms if needed.
   • Focus on wave V to SN10 amplitude rather than wave III for reliable ear-specific interpretation.
6. Clinical Application:
   • Use primarily in infants and children under 2 years.
   • Avoid in patients with contraindications (e.g., VP Shunts).
   • Perform direct testing on both ears regardless of contralateral response.

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Speakers / Sources Featured

• Inga Ferm – Audiologist and expert interviewed in the video, providing detailed explanations and clinical insights on Two-Channel Bone Conduction ABR Testing.

Category

Educational

Video