Electrically Evoked Auditory Brainstem Response over Round Window by Bipolar Stimulation

Auditory brainstem potentials can be elicited by electrical stimulation of the round window (RW). In this technique, extracochlear stimulation is objectively used in the selection of cochlear implant (CI) candidates to avoid cochlear damage. However, until now, its use is limited due to the large artifacts generated by electrical stimulation. Our objective was to obtain reliable and reproducible electrically evoked auditory brainstem responses (eEABRs) using a new method of stimulation.

This was a prospective study including subjects who underwent electrical stimulation on RW during CI surgery between 2013 and 2016. A "Stimulator Box," which produces electric stimuli identical to those provided by a CI, and an evoked potential recording equipment were used. The results obtained with monopolar and bipolar electrodes were compared.

RW eEABR recordings of 49 subjects (mean age, 34 years) were characterized by their stability and by having wave V between 3 and 5.5 ms. A higher percentage of responses were obtained on increasing the phase duration instead of the pulse amplitude. A significantly greater percentage of positive responses were obtained using bipolar stimulation than using monopolar stimulation (p<0.001).

Using extracochlear electrical stimulation technique, described herein, and bipolar electrical stimulation probe allows for reliable and reproducible eEABR recordings in CI candidates.