Improvised explosive devices (IEDs; commonly used as roadside bombs) are a common cause of combat injury in the wars. They are also often used as weapons, inflicting severe injuries on non-combatants around the world, including within the United States. When an explosive detonates, high pressure gasses are released that expand away from the point of detonation. This compresses the surrounding air and produces both a blast wave and a blast wind that propagate away from the explosion in a spherical pattern. The high energy forces associated with these components of a blast can produce devastating trauma upon soldiers and civilians in its vicinity. Damage to the ear is the most common consequence of a blast exposure
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There are four different mechanisms of bodily damage after blast exposure. Primary blast injury is caused by the direct effect of the high pressure wave upon the tissue. Secondary blast injuries occur when the blast wind propels shell fragments or debris into the tissue. Tertiary blast injury is when the blast wind knocks down or blows the individual into a solid object. Quaternary blast injuries include all other effects, such as post-traumatic stress disorder or burns.
While lethal blast pressures for humans are roughly 414–552 kPa, there is a 50% rate of tympanic membrane perforation with blast pressures of only 104 kPa. Damage to the ear is an incredibly prevalent condition and over 60% of wounded-in-action service members have eardrum injuries, tinnitus, and/or hearing loss.
Primary blast injuries of the auditory system cause significant morbidity, but are easily overlooked. Injury is dependent on the orientation of the ear to the blast. TM perforation is the most common injury to the middle ear. Signs of ear injury are usually present at time of initial evaluation and should be suspected for anyone presenting with hearing loss, tinnitus, otalgia, vertigo, bleeding from the external canal, TM rupture, or mucopurulent
otorhea. All patients exposed to blast should have an otologic assessment and audiometry.