Noninvasive indirect intracochlear pressure monitoring during cochlear implantation

Outcomes following cochlear implantation remain highly variable, particularly with respect to hearing preservation. While surgical techniques aim to minimize intracochlear trauma, no objective intraoperative method currently exists to monitor intracochlear pressure dynamics. We present a feasibility study of indirect, noninvasive monitoring of intracochlear pressure using a calibrated probe microphone positioned in the external auditory canal. Measurements were performed in fresh-frozen temporal bones and during five clinical cochlear implantation procedures. Ear-canal pressure signals were transformed using a reverse middle-ear transfer function to estimate intracochlear pressure in the scala vestibuli, and sound pressure levels were derived to characterize acoustic exposure during surgical stages. Transient high-amplitude events were observed throughout the procedure. Round window opening produced peak intracochlear pressures exceeding 140 dB SPL. Electrode array insertion generated peak levels between 132 and 172 dB SPL, consistent with direct intracochlear measurements, supporting the validity of the approach during insertion. Post-insertion implant management produced pressures comparable to or exceeding insertion, indicating substantial acoustic exposure. Drilling and suction during mastoidectomy resulted in very high estimated levels (up to 178 dB SPL); however, these measurements are affected by contamination from airborne and structure-borne noise. Ex vivo experiments demonstrated temporally correlated responses between ear-canal recordings and a mechanically coupled sensor, supporting a middle-ear transmission pathway. These findings demonstrate the feasibility of noninvasively capturing acoustic signatures during cochlear implantation and support the development of intraoperative noise dosimetry to optimize hearing-preservation techniques.