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 operati on, audiograms were taken before and after surgery. The aim was to det ect 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. Si x days post-operatively they were re-examined and asked about their he aring and any tinnitus. Various operative details were taken and the p ost-operative drug record examined. Patients who were too ill for rete sting, or who had been given sedative or ototoxic drugs or opiate anal gesia, were dropped from the study. Twenty patients completed the test s. The whole procedure was repeated on a control group of 20 patients who were having thorocotomy but without being placed on a cardiopulmon ary bypass. From the bypass sample of 40 ears, five ears (four individ uals) had an individually statistically significant high-frequency hea ring loss. The results show a statistically significant difference bet ween the bypass group and the control group, with the bypass patients having worse threshold shifts folio wing the operation. Discriminant a nalyses have shown that those patients suffering hearing impairment ma y be discriminated principally with four variables: the patient's age, minimum temperature and minimum blood pressure during the operation, and the time on bypass.