Changes of Electrocochleographic Responses During Cochlear Implantation Presented at the Annual Meeting of ADANO 2016 in Berlin.

OBJECTIVE: To assess by electrocochleography (ECoG) at which times during cochlear implantation changes of cochlear function occur. METHODS: Tone bursts with a frequency of 500 or 750 Hz were used as acoustic stimuli. The recording electrode was placed on the promontory and left in an unchanged position for all ECoG recordings. RESULTS: Eight subjects were included. After opening the cochlea, an increase of the amplitude of the ECoG signal was detectable in four subjects (mean change 3.9 dB, range from 0.2 to 10.8 dB). No decreases were detectable after opening the cochlea or during the first half of the insertion of the CI electrode array (mean change 0.5 dB, range from -2.2 to 1.6 dB). During the second half of the insertion, the amplitude of the ECoG signal decreased in four subjects (mean change -2.5 dB, range from -0.04 to -4.8 dB). If a decrease occurred during the second half of the insertion, then the decrease continued in the earliest phase after insertion of the CI electrode array (mean change -2.1 dB, range from -0.5 to -5.8 dB). CONCLUSION: Pressure changes inside the cochlea can lead to an increase of ECoG signals after opening the cochlea. If detectable, then a decrease of ECoG signals occurs during the second half of the insertion of the CI electrode array and continues in the earliest phase after completed insertion. These findings suggest that cochlear trauma occurs toward the end of the insertion and that trauma-dependent postoperative mechanisms contribute to postoperative hearing loss.

Electrocochleographic Responses Before and After Short-Term Suprathreshold Electrical Stimulation in Human Cochlear Implant Recipients.

OBJECTIVE: To assess changes in electrocochleographic (ECoG) responses following short-term suprathreshold electrical stimulation during cochlear implant (CI) telemetry in CI recipients. METHODS: Extracochlear ECoG recordings were conducted before and after intraoperative short-term suprathreshold electrical stimulation. Tone bursts at 500, 750, and 1000 Hz as well as clicks were used as acoustic stimuli. Changes of ECoG responses were correlated to calculated maximum electrical charge levels. RESULTS: Fourteen subjects were included. On average, no significant changes of ECoG responses occurred in the earliest postoperative phase; therefore, also following short-term suprathreshold electrical stimulation. However, one subject (S7) showed a decrease of ECoG responses. Neural as well as hair cell components of the ECoG signal were affected. On average, the maximum electrical charge level was 22 nC (range, 15-37 nC). In S7, the maximum electrical charge level was 17 nC. No correlations were found between maximum electrical charge levels and changes of ECoG signals. CONCLUSION: In a majority of cases, electrophysiological responses to acoustic stimuli remain unchanged in the earliest postoperative phase. However, deterioration of cochlear function occurs in this phase. Neural as well as hair cell components of the ECoG signal are affected. Such deterioration is not associated with unusually high electrical charge levels during CI telemetry. Overall, our results support the notion that an electrical charge applied at levels used in the clinical routine does not have an acute deleterious effect on cochlear function.

Assessment of Cochlear Function during Cochlear Implantation by Extra- and Intracochlear Electrocochleography.

Objective: The aims of this study were: (1) To investigate the correlation between electrophysiological changes during cochlear implantation and postoperative hearing loss, and (2) to detect the time points that electrophysiological changes occur during cochlear implantation. Material and Methods: Extra- and intracochlear electrocochleography (ECoG) were used to detect electrophysiological changes during cochlear implantation. Extracochlear ECoG recordings were conducted through a needle electrode placed on the promontory; for intracochlear ECoG recordings, the most apical contact of the cochlear implant (CI) electrode itself was used as the recording electrode. Tone bursts at 250, 500, 750, and 1000 Hz were used as low-frequency acoustic stimuli and clicks as high-frequency acoustic stimuli. Changes of extracochlear ECoG recordings after full insertion of the CI electrode were correlated with pure-tone audiometric findings 4 weeks after surgery. Results: Changes in extracochlear ECoG recordings correlated with postoperative hearing change (r = -0.44, p = 0.055, n = 20). Mean hearing loss in subjects without decrease or loss of extracochlear ECoG signals was 12 dB, compared to a mean hearing loss of 22 dB in subjects with a detectable decrease or a loss of ECoG signals (p = 0.0058, n = 51). In extracochlear ECoG recordings, a mean increase of the ECoG signal of 4.4 dB occurred after opening the cochlea. If a decrease of ECoG signals occurred during insertion of the CI electrode, the decrease was detectable during the second half of the insertion. Conclusion: ECoG recordings allow detection of electrophysiological changes in the cochlea during cochlear implantation. Decrease of extracochlear ECoG recordings during surgery has a significant correlation with hearing loss 4 weeks after surgery. Trauma to cochlear structures seems to occur during the final phase of the CI electrode insertion. Baseline recordings for extracochlear ECoG recordings should be conducted after opening the cochlea. ECoG responses can be recorded from an intracochlear site using the CI electrode as recording electrode. This technique may prove useful for monitoring cochlear trauma intraoperatively in the future.