Measurement of sound emission by endoscopic lithotripters: an in vitro study and theoretical estimation of risk of hearing loss in a fetus.

BACKGROUND: There is concern about applying intraureteral lithotripsy in pregnant patients, as the sound created by the equipment may damage fetal hearing. MATERIALS AND METHODS: The sound intensities produced by electrokinetic, pneumomechanic, holmium laser, ultrasound, and electrohydraulic intraluminal lithotripters were measured in an in vitro model. RESULTS: The purely mechanical modalities (electrokinetic and pneumomechanic) generated lower peak pressures than the other devices. Theoretical calculations were performed based on the fact that in vivo, the sound path and the fetal middle ear cavities are filled with fluid. Calculated pressure levels that give displacement amplitudes of the tympanic membrane, the ossicles, and the basilar membrane comparable to hearing loss risk criteria for airborne impulsive noise are greater than measured for all of the lithotripters. The fluid-filled middle ear thus seems to give the fetus protection against sound. The fluid also improves the symmetry of the cochlea structure, reducing the influence of direct bone transmission. CONCLUSIONS: The peak pressure of the sound emitted by lithotripsy in the ureter during pregnancy is unlikely to be harmful to fetal hearing. Other risk factors, such as the form of the sound waves and the pulse duration were not evaluated. The theoretical assessments are simplified, and one should be careful about drawing conclusions from theoretical considerations and calculations alone.

Brainstem-evoked responses of guinea pigs exposed to high noise levels in utero.

Pregnant guinea pigs were exposed to loom room noise at 115 dB A for 7.5 hr/day for various periods during the last one-third of pregnancy. When the hearing of their offspring was tested by auditory brain stem-evoked response techniques at 6-dB intervals, peak IV latencies of exposed pups were found to be significantly longer than those of otherwise similar control pups. The latency differences corresponded to a 5-dB increase in stimulus at medium stimulus levels and 10-12 dB near threshold. The results indicate that it is possible for noise-induced loss to occur in utero in mammals whose auditory maturation process is complete, or nearly so, before birth.