EFFECT OF DRILL INDUCED NOISE DURING MASTOID SURGERY ON HEARING STATUS OF CONTRALATERAL EAR

BACKGROUND Hearing morbidity of a healthy ear resulting from drill induced noise while operating the diseased may add on to the actual morbidity arising due to an unhealthy ear. We wanted to study the effect of drill induced noise during mastoid surgery on hearing status of contralateral non-operated ear. METHODS This was a prospective interventional study. 64 patients were enrolled in the study. Audiological tests on patients were done postoperatively after 6 hours, 48 hours, 72 hours, 96 hours and 6 months. RESULTS Most subjects (40.62 %) were in the age group of 10-20 years while only 7.81% subjects were >= 40 years of age. Demographic statistics revealed that majority of the cases were Hindus (92.12%) followed by Muslims (7.81%). PTA revealed that hearing thresholds were not affected at lower frequencies of 250-1000 Hz unlike observations at 4 KHz, 6 KHz and 8 KHz which reflected a certain change though did not differ significantly between time points. Mean hearing threshold changes, considering all frequencies, were 4.4 dB after 6 h, 4.48 dB after 48 h, and 9.1 dB, after 72 h of the surgery which was statistically significant at 6 KHz and 8 KHz. In the present study, the hearing improvement after surgery was considered successful as the air-bone gap closure of >= 10 dB was noted in 52 cases (81.25%) with the average air-bone gap closure being 15.2 dB on PTA done at 3 months post operatively. CONCLUSIONS A wise choice of operative technique and improving range and quality of drilling equipment can be helpful in reducing the morbidity load effectively. Tympanomastoid surgery and drilling during ear surgery has the potential to cause significant acoustic trauma and transient sensory hearing loss in the contralateral ear. Though drill-generated noise cannot be reduced to any great extent, still in order to lower the acoustic trauma in an ear surgery to the contralateral ear, parameter of burr and drill must be known preoperatively.