Intracochlear Pressure Measurements Quantify Overall Noise Exposure to the Inner Ear During Mastoidectomy

The acoustic exposure patients endure during otologic surgery is unclear, as previous studies have not captured the effects of vibrational noise on the inner ear. To fill this knowledge gap, we examined inner ear noise directly via intracochlear pressure changes during mastoidectomy and cochleostomy.

Inner ear stimulation was measured using fiber optic pressure sensors inserted into the cochlea of cadaveric heads using a transcanal approach. A tympanomeatal flap was elevated, cochleostomies were made into scala vestibuli and tympani, sensors were placed and secured to the cochlear promontory, and the flap was resecured. Intracochlear pressures were measured with different drill bits, speeds, and during mastoidectomy and cochleostomy. The equivalent sound pressure level in the ear canal (L Eq ) was calculated using the middle ear transfer function. Microphones were also placed in the surgeon's ear, the cadaver ear, and ~3 feet away.

Results show sound pressure levels that could exceed 120 dBA (A-weighted dB SPL L Eq ), with the highest levels observed during cochleostomy. Results showed broadband exposure, with a distinct peak at 1.33 kHz during the 80k RPM drill speed. Importantly, SPLs in the surgeon's ear did not always predict patient noise exposure.

Surgically induced cochlear noise revealed levels high enough to potentially induce acoustic trauma and sometimes at frequencies that may cause hearing loss not captured by a traditional audiogram (ie, 1.33 kHz). These data characterize surgical noise exposures and will lead to permissible noise exposure guidelines and durations for both patients and surgeons.