Tympanic Membrane Perforation and Hearing Loss From Blast Overpressure in Operation Enduring Freedom and Operation Iraqi Freedom Wounded

Primary blast injury is tissue destruction caused by the blast wave of high-pressure air that travels outward from an explosion. Tympanic membrane (TM) rupture is the most common form of primary blast injury. Since the ear is, by design, the body's most sensitive pressure transducer, it is the organ most commonly affected by the dramatic changes in ambient air pressure that occur close to an explosion. Studies of service members injured in combat have demonstrated that TM perforation occurs in approximately 9% of patients wounded by explosives. (Ritenour AE, Blackbourne LH, Kelly JF, et al. Primary blast injury in OEF/OIF: 2003 2006. Unpublished data.) TM rupture occurs more frequently when an explosion takes place in a closed space and when victims are in close proximity to the detonation center. The lowest pressure necessary to perforate a TM is about 5 psi; approximately 50% of TMs will rupture at 15 psi. Various factors have proven to positively or negatively affect an individual's susceptibility to TM rupture. Studies have demonstrated that disease or previous injury, increased age, inadequate pneumatization, and TM position perpendicular to the incident wave all increase the likelihood of perforation. Conversely, plugs of cerumen may exert a protective effect when loose in the external auditory canal, but may serve as a ramrods increasing injury if they are in contact with the TM at the time of the explosion. Simple ear plugs are very effective in reducing the incidence of TM rupture, but are impractical in situations, such as combat, where accurate understanding of quiet verbal communication is critical. Investigators have demonstrated that up to 80% of all perforated TMs heal spontaneously with relatively few requiring operative intervention. Large size of perforation (high grade) and peripheral location of the defect have both been associated with lower rates of spontaneous healing. Published in the Jnl. of Trauma Injury, Infection, and Critical Care Feb Supplement 2008 pS174-S178.