A study of the effects of cardiopulmonary bypass surgery on auditory function.

Cardiopulmonary bypass surgery is commonplace in many medical centers and rare instances of unilateral hearing loss in these patients have been reported and have been attributed to embolism. Two more patients are reported and their discovery prompted a study of pre and postoperative hearing in 68 patients at Newark Beth Israel Medical Center, where a single team performs the cardiopulmonary bypass surgery. Previous similar studies showed no changes following CPB surgery. Almost all patients have been male and prolonged pump times (over 150 min.) were noted in 7 of 11 reports. Based on changes in hearing found on pre and postoperative testing in the 6 patients, 3 groups were developed: those with no change and those with slight changes were compared with those having average deficits of more than 10 db. Prolonged pump times occurred only twice in the series and were not associated with loss. A second milder form of hearing loss, which was bilateral and affected the high tones, was noted in significant numbers. Two of these patients had persistent tinnitus after surgery. Although the series is small, there appears to be an increased susceptibility in males to the development of high tone loss as well. Based on the preponderance of males, with their high incidence of basilar artery atherosclerosis, and the frequent prolonged pump times, perfusion failure seems to be the most likely etiology for the rare cases of hearing loss accompanying cardiopulmonary bypass surgery.