A sudden exposure to an intense sound (e.g. a gunshot, fireworks, music) may cause hearing impairment or ringing in the ears.
The most important part of treatment is future hearing protection in order to prevent permanent hearing loss.
Epidemiology
Of teenagers, 20-50% experience exposure to noise levels high enough to cause acute acoustic trauma.
During military service, 1-2% of conscripts sustain acute acoustic trauma.
During hunting activities, acoustic trauma is mainly associated with gun sports and particularly with accidental shots.
Mechanism
An intense sound wave will cause damage to the inner ear structures. Noise can also cause inner ear hypoxia which destroys sensory cells by disturbing their metabolic processes.
When the loudness of a sound exceeds 165 dB, the pressure wave may also rupture the tympanic membrane.
Signs and symptoms
Blocked ear, stuffiness in the ear, hearing impairment, humming or ringing noises. Bleeding from the ear is possible if the tympanic membrane has ruptured.
If the tympanic membrane is intact, the otoscopic finding will usually be normal. Testing with a tuning fork (size C5) may be suggestive of inner ear injury, but a formal hearing test is indicated in all suspicious cases.
An audiogram will show changes consistent with inner ear injury typically in the 3-6 kHz frequency range.
Treatment
Treatment primarily focuses on the reduction of future exposure, i.e. the patient should avoid all excessive noise and loud sounds.
Medication that aims to improve the inner ear damage is available (prednisolone 1-2 mg/kg/day for 7 days; betahistine). There is very little reliable evidence on their use.
More serious cases should be referred to specialist care. Hyperbaric oxygen therapy Hyperbaric Oxygen Therapy (HBOT) is a possible treatment option, and it has been used to treat acoustic trauma in military service conscripts.
Smoking should be stopped.
An individual who has sustained severe hearing loss as a result of an acoustic trauma is not suitable for work involving noise exposure. The prohibition is not absolute, but there may be a statutory obligation to monitor the person's hearing impairment, for example by annual checks for the first three years. If the hearing impairment does not worsen, it may be possible to continue with checks every three years.
Prognosis
Each episode of acoustic trauma results in permanent damage within the inner ear, even though in the majority of patients the symptoms will disappear and an audiogram will show normal hearing within a few hours to a few days.
In some cases, the changes seen in the audiogram will only partially improve or remain permanent.
Tinnitus Tinnitus may persist for a long time. In some cases, tinnitus may become a permanent condition and affect the person's quality of life.
Education regarding the harmful effect noise has on hearing is of the utmost importance.
Avoidance of exposure to noise is very important.
The use of hearing protectors is necessary if exposure to impulse noise can be expected.
The noise attenuating effect of single use earplugs is similar to that of earmuffs, but the correct insertion of earplugs requires practice and the attenuation they provide may therefore be worse than with earmuffs. If the noise exposure is very intense, the combined use of earplugs and earmuffs is recommended.