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Auditory monitoring for preservation of the function of the auditory nerve

Auditory monitoring for preservation of the function of the auditory nerve. Recording of auditory evoked potentials in operations in the posterior fossa. Different conventions for display of ABR. NEURAL GENERATORS OF ABR:. Peak I: distal auditory nerve Peak II: central auditory nerve

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Auditory monitoring for preservation of the function of the auditory nerve

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  1. Auditory monitoring for preservation of the function of the auditory nerve Recording of auditory evoked potentials in operations in the posterior fossa

  2. Different conventions for display of ABR

  3. NEURAL GENERATORS OF ABR:

  4. Peak I: distal auditory nerve • Peak II: central auditory nerve • Peak III: mainly cochlear nucleus • Peak IV: unknown • Peak V: termination of • the lateral lemniscus in the contralateral inferior colliculus

  5. Intraoperative monitoring of auditory evoked potentials • Interpretable response must be obtained in the shortest possible time • Techniques are different from clinical use of ABR

  6. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  7. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  8. Effect of stimulus rate on amplitude of ABR

  9. Gain from increasing the stimulus rate

  10. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  11. Earphones

  12. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  13. Auditory brainstem evoked potentials (ABR):The latencies of the peaks are importanttherefore: Enhance the peaks by using optimal filtering

  14. Digital filtering can enhance the waveform of the ABR

  15. Recording parameters for obtaining an interpretable responses in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  16. Dipoles of ABR

  17. Recording parameters for obtaining an interpretable ABR in the shortest possible time: High stimulus rate High sound intensity Optimal filtering Optimal electrode placement Reduction of electrical interference

  18. Find the source of interference

  19. Recording directly from the auditory nerve Provides nearly instantaneous monitoring of neural conduction in the auditory nerve

  20. Cotton wick recording electrode

  21. ABR: Vertex-neck Earlobe-earlobe Auditory nerve:

  22. ABR Vertex-neck Unfiltered Filtered CAP from CNVIII Distally Near brainstem

  23. Response from auditory nerve Normal CAP Injury from heat

  24. Before surgical manipulations After surgical manipulations Solid lines: Rarefaction clicks Dashed lines: Condensation clicks

  25. Waveform of the CAP recorded from the exposed CNVIII depends onpre-existing hearing loss

  26. The recording electrode is difficult to keep in place on the CNVIII Recording from the surface of the cochlear nucleus

  27. Recording from the cochlear nucleus: Recording electrode is placed in the lateral recess of the fourth ventricle

  28. ELECTRODE WIRE UNDER DURA SUTURES CN IX & CN X ELECTRODE WIRE CHOROID PLEXUS TUMOR CN VIII FLOCCULUS FORAMEN OF LUSCHKA WICK ELECTRODE FROM: MOLLER ET AL 1994

  29. Auditory nerve injuries affect speech discrimination more than cochlear injuries

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