Intracochlear pressure measurements quantify overall noise exposure to the inner ear during mastoidectomy
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Introduction
The acoustic trauma patients are exposed to 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 a mastoidectomy and cochleostomy.
Methods
Inner ear stimulation was measured using fiber optic pressure sensors inserted into the cochlea of cadaveric heads using a trans-canal approach. A tympanomeatal flap was elevated, cochleostomies were made into scala vestibuli and tympani, and sensors placed and secured to the cochlear promontory, and the flap 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, cadaver ear, and approximately three feet away.
Results
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 broad band 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.
Conclusion
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 (i.e. 1.33 kHz). This data characterizes surgical noise exposures, and will lead to permissible noise exposure guidelines and durations for both patients and surgeons.
