Intraoperative Cochlear Response Telemetry (CRT) to Assess Hearing Preservation

Background: To reduce possible intracochlear damage of hair cells and preserve existing residual acoustic hearing, over the last decades different CI designs have been developed (e.g. short, straight or pre-curved arrays). Besides surgical technique enhancements such as increasing duration or reducing speed of electrode insertion, previous studies have also suggested that electrocochleography (ECochG) might be a tool to monitor acoustic hearing preservation during electrode insertion.
Objective: To obtain intra- and postoperative ECochG responses, using a dedicated research tool developed by the University of Melbourne and Cochlear Limited (Cochlear Response Telemetry (CRT),) to evaluate ECochG variables, cochlear microphonics (CM) and to examine whether there is an association between change in CM and post-operative hearing preservation.
Methods: Prospective study in selected group of CI candidates with significant low frequency residual hearing (i.e. ≤ 80 dBHL at 500 Hz). Intra- and postoperative acoustic ECochGs are performed in CI patients using CRT software tool to obtain ECochG variables (CAP, SP, CM). Additionally, preop outer hair cell activity of patients is assessed using otoacoustic emissions, especially for 500 Hz.
Results: Intra- and postop patient data show that CRT is a dedicated software tool to stimulate, average and obtain CAP, SP and CM. Our intra- and postop results show reliable and reproducible CM recordings that are perfectly time-locked to insertion time and speed within acceptable signal-noise ratios.
Conclusions: The CRT research tool is of great value for intraoperative monitoring of cochlear neural processing. When related to postop hearing evaluation, real-time feedback through CRT monitoring may help surgeons to optimize insertion procedures.