gms | German Medical Science

Introduction: Recently designed cochlear implant electrodes aim to preserve the residual hearing during implantations, succeeding in most cases. For the remaining cases the question arises whether the impairment is caused by the intrinsic surgery or by processes initiated postoperatively.

Methods: Within the implantation routine of devices aiming to preserve the residual hearing Auditory Steady State Responses (ASSR) were registered intraoperatively. Therewith the hearing threshold was evaluated under anaesthesia directly before and after surgery. Up to now registrations were done with 107 subjects (41 m, 66 f, Ø 54.8 yrs). 34 of them were implanted with a Nucleus Hybrid-L electrode, 61 with a Nucleus SRA electrode and 12 with a MedEl FlexEAS electrode. The obtained ASSR thresholds were compared with each other and with the pre- and postsurgically measured behavioural thresholds.

Results: On average, the difference between pre- and postsurgically measured behavioural thresholds was 11.4 dB ± 14.8 dB (mean ± standard deviation), the difference between pre- and postsurgically obtained ASSR thresholds was 5.0 dB ± 13.1 dB, the difference between presurgically obtained behavioural and ASSR thresholds was 17.2 dB ± 14.5 dB and the difference between postsurgically obtained behavioural and ASSR thresholds was 15.0 ± 20.4 dB.

Conclusion: The ASSR thresholds were found to be highly reproducible before and after surgery. Thus, the method can be applied for the desired purpose. The differences between ASSR thresholds were detected to be smaller than the differences between the behavioural thresholds. This indicates that impairments of the residual hearing during surgery are primarily caused by postoperative processes.