Hearing loss in HEMS operations: a prospective analysis of audiometric tests for temporary hearing threshold shift of an air rescue helicopter crew during several days of emergency duty.

BACKGROUND: Helicopter Emergency Medical (HEMS) crews are exposed to varying levels of noise at work. Noise levels regularly exceed 85 dB(A) and can be as high as 108 dB(A). Noise exposure can reduce concentration and cause hearing damage. The present study was conducted to assess objective Hearing sensitivity shift of air rescue crews. METHODS: Audiometric data of HEMS crew of an Airbus EC 135 were collected during two months of duty at frequencies from 500 to 8000 Hz. Audiometric tests were performed at the beginning and end of a shift and, if possible, thirty minutes after every HEMS operation. Crew members were asked to complete a questionnaire before every measurement on ringing in the ears and exposure to elevated noise levels without hearing protection. Results of the audiometric measurements were analysed using linear mixed models for the whole group and for subgroups of pilots and medical personnel with and without additional hearing protection. RESULTS: On 17 days with a median daily number of 6 HEMS flights, a total of n = 236 audiometric tests were conducted for 18 crew members, of whom four (22%) were pilots and fourteen (78%) were medical personnel. The mean noise exposure duration was 169.9 (± 49.2) minutes. The mean flight duration was 50 (± 40.2) minutes. Across all subgroups, subjects were able to hear a test tone at a mean level of 8.2 (± 11.1) dB(A) at the beginning of a shift and 11.7 (± 12.1) dB(A) at the end of a shift. The initial difference of hearing threshold between the left and the right ear was evened out over the work shift (beginning β = 2.9 p < 0,001vs. after noise exposure 0.2, p = 0.434). Hearing threshold shift was greater in medical personnel who wore no additional hearing protection (6.8 dB(A)) than in pilots (1.9 dB(A)) and medical personnel who used additional hearing protection (0.5 dB(A)). The greatest hearing threshold level occurred at frequencies between 4000 and 8000 Hz. CONCLUSIONS: Hearing sensitivity of HEMS crews substantially declines over the course of a shift. Unprotected medical personnel seems more affected than pilots. Hearing threshold level is greater in left ears than in right ears and most severely affects the ability to hear high-frequency sounds. Helmets alone may not provide adequate hearing protection.