Introduction: Preservation of residual hearing is essential to perceive acoustic stimulation from hybrid cochlear implants (CI). Preservation is a good marker of atraumatic surgery and residual hearing may be exploited further or enhanced in future therapies, making complete hearing preservation a desirable goal for all current CI surgeries. There is large variability in the amount of hearing preserved and the timeframe over which it is lost after CI. The increase in numbers of patients with high levels of residual hearing at implantation means that understanding the variables affecting its preservation is more important than ever.
Data sources: An English search term with generic and specific items concerning hearing preservation and cochlear implantation was searched on the Web of Science service. The search timeframe was limited to 2000 to 2014, with no language limitations on results.
Study selection: Hearing preservation, retrospective CI outcome studies which reported pre- and post-surgical pure-tone audiometry (PTA) were identified and selected.
Data extraction: PTA thresholds were extracted from audiograms or tables and converted into a low-frequency hearing preservation (LFHP) score. Data for 21 factors associated with hearing preservation were collected from studies.
Data synthesis: Factors were included in a hearing preservation model if they had both a significant bivariate correlation with LFHP and a significant Kruskal-Wallis H test result (for ordinal data) or a significant multiple regression analysis result (for scale data).
Conclusions: Seven factors were found to have a significant effect on hearing preservation: insertion site, progressive versus stable hearing loss, insertion angle of electrode, use of intraoperative topical steroids, use of steroids (via any route/timing), hearing etiology, and electrode array type. The best hearing preservation options are given.