Effect of aspiration of perilymph during stapes surgery on the endocochlear potential of guinea pig

Objective. Suction applied to the vestibule through the oval window during stapes surgery is considered a primary risk for postoperative sensorineural hearing impairment. This study investigated the mechanism of acute phase change in cochlear function caused by aspiration of the opened oval window. Study Design. Guinea pig model. Setting. Academic hospital laboratory. Subjects and Methods. Guinea pigs were divided into 3 groups: stapes footplate removed without suctioning (6 animals), with indirect suctioning (5 animals), and with direct suctioning of the vestibular perilymph (6 animals). Endocochlear potentials (EPs) were measured at the second turn of the cochlea, and temporal bones were examined histologically. Results. Removal of the stapes footplate without suctioning caused little change in the EP (original value, 80.12 ± 3.52 mV), indirect suctioning caused minor decline of the EP of 9.14 ± 1.84 mV, and partial recovery ensued, whereas direct but gentle suctioning, resulting in dry vestibule, caused reduction in the EP of 16.38 ± 6.63 mV. Recovery was not observed or incomplete. No animals showed profound decrease in the EP. Conclusion. Gentle suctioning and removal of the vestibular perilymph can cause a mild decrease in the EP even without damaging the inner ear structures. Therefore, suctioning of the perilymph should be avoided during stapes surgery because acute hearing loss can result even without damaging the inner ear structures. However, hearing loss may not be profound, if suctioning is not vigorous enough to cause damage to the inner ear structures.