Audiometric changes in patients undergoing coronary artery bypass surgery.

The incidence of severe hearing loss following coronary artery bypass surgery has been estimated as one per thousand (Plasse et al., 1981). To evaluate the audiological changes that may be caused by the operation, audiograms were taken before and after surgery. The aim was to detect losses that were not necessarily severe and to examine the factors associated with any auditory insult. Patients without a past medical history of hearing problems or ototoxic drugs were examined on the day prior to the coronary bypass operation and audiometry carried out. Six days post-operatively they were re-examined and asked about their hearing and any tinnitus. Various operative details were taken and the post-operative drug record examined. Patients who were too ill for retesting, or who had been given sedative or ototoxic drugs or opiate analgesia, were dropped from the study. Twenty patients completed the tests. The whole procedure was repeated on a control group of 20 patients who were having thorocotomy but without being placed on a cardiopulmonary bypass. From the bypass sample of 40 ears, five ears (four individuals) had an individually statistically significant high-frequency hearing loss. The results show a statistically significant difference between the bypass group and the control group, with the bypass patients having worse threshold shifts following the operation. Discriminant analyses have shown that those patients suffering hearing impairment may be discriminated principally with four variables: the patient's age, minimum temperature and minimum blood pressure during the operation, and the time on bypass.