Abstract
BackgroundSudden sensorineural hearing loss is routinely encountered by the otologist. The etiology is varied and often identifiable. One of the relatively less frequent causes is surgery. Apart from being an established entity with otological surgeries, sensorineural hearing loss has also been known to occur after non-otological procedures under general anesthesia. Commonest amongst these procedures is cardiopulmonary bypass, an association that has long been recognized. However, despite the proposition of diverse hypotheses in the past, the pathophysiology remains unclear.MethodsThe study is a prospective matched cohort study that will be carried out in Aga Khan University Hospital, Karachi, Pakistan. Participants among exposed would include all those patients who would be undergoing coronary artery bypass surgery in the hospital who fall under the criteria for inclusion. Unexposed group would comprise of patients undergoing a non-bypass procedure of similar duration under the same type of anesthesia who meet the selection criteria. Both these groups will undergo audiometric testing at our hospital on three different occasions during the course of this study. Initially before the procedure to test the baseline hearing capacity; then one week after the procedure to assess any changes in hearing ability following the surgery; and finally a third audiogram at six weeks follow-up to assess further changes in any hearing deficits noted during the second phase of testing. Certain variables including the subjects' demographics and those concerning the procedure itself will be noted and used later for risk factors analysis. A detailed past medical and surgical history will also be obtained. Data analysis would include calculation of relative risk and significance of the results, by running the chi-square test. Other statistical tests like Fisher exact test may then be employed to facilitate data interpretation. Continuous scale may then be employed and multivariate linear regression used.DiscussionThis study is planned to obtain a better understanding of the correlation between sudden sensorineural hearing loss and cardiopulmonary bypass. Being the first major cohort trial in this line of investigation, the project is designed to identify the existence of any significant relationship between cardiopulmonary bypass and sensorineural hearing deficit.
Highlights
Sudden sensorineural hearing loss is routinely encountered by the otologist
Even more traumatizing is the development of a sudden sensorineural hearing loss by a patient, a disease afflicting 1 in every 5000 patients in the general population [1]
Earlier Brownson et al (1971) [3] had tried unsuccessfully to achieve the same in a prospective study with a limited sample. This was followed by a larger retrospective study by Plasse et al [4,5] in which he evaluated 7000 patients and found the incidence of Sensorineural hearing loss (SNHL) with aortocoronary bypass surgery to be 1 in 1000 (0.1%)
Summary
Study design This is a prospective matched cohort study. Setting Aga Khan University Hospital, Karachi, Pakistan. Inclusion criteria for unexposed group All patients who qualify for the criteria of being age and sex matched with the exposed (on an individual basis) undergoing a non-cardiac and non-otologic surgery under general anaesthesia, of similar time duration, who give consent and comply with the testing. The questionnaire will make note of patient demographics and various questions that comprise an otologic and past medical and surgical history asked to determine if the patient had any prior hearing loss, ear disease, ear surgery, known ototoxic medication usage, tinnitus, vertigo, family history of hearing loss, noise exposure, neurological disease, diabetes, hyperlipidemia, hypertension and hypotension After the procedure it will be inquired if the patient had the subjective complaint of hearing loss, tinnitus, vertigo, imbalance, any ear pain or discharge. Data analysis will be carried out, in case of usage of continuous variables, by multivariate linear regression
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