July 11, 2006 Feature

Blast-Related Ear Injury in Current U.S. Military Operations

Role of Audiology on the Interdisciplinary Team

U.S. Military
Photo credit: Tech Sgt. John M. Foster, U.S. Air Force

In the 16th century, the French surgeon Ambroise Paré reported "… a great thunderous noise, large bells or artillery, and thus one often sees gunners losing their hearing whilst drawing the machinery because of the great agitation of the air inside the ear which breaks the aforementioned membrane and moves to the bones known as ossicles out of their natural position: so that the air is implanted or absorbed within the sinuses of the mastoid cavity and the patient has a continuous noise and air within the ear." (Mudry, 1999). Five centuries later, noise-induced hearing loss and ear injury continues to be inextricably linked to military service, particularly in time of war.

Disease and non-battle injuries (e.g., accidents, illnesses, etc.) account for the majority of medical evacuations from current combat operations in Iraq and Afghanistan, while battle injuries account for only about 14% of all evacuations. This trend is similar to previous recent military conflicts. However, the survival rate of those wounded in current conflicts exceeds 88%-a significant improvement over the 78% survival rate of those wounded during the Gulf War in 1990. This increased survivability is largely attributed to improved protection of body and vehicle armor and rapid medical attention for injured personnel.

The proportion of blast-related injuries seen from Iraq and Afghanistan, however, is higher than in previous wars (see Table 1 below). About 68% of all wounded-in-action (WIA) evacuations are for blast-related injuries due to the enemy's weapons of choice-improvised explosive devices (IEDs) and rocket-propelled grenades (RPGs). As a result, although more wounded soldiers are surviving injuries that would have been fatal in previous wars, the nature and extent of those injuries tend to be more severe and require complex long-term medical management.

Table 1. Percentage and type of wounded-in-action (WIA) injuries to U.S. service members in current and previous wars.
Explosion Gunshot Wounds Other
Operation Iraqi Freedom
68%
15%
17%
Korean War
54%
27%
19%
WW II
64%
19%
17%

Between March 2003 and October 2005, the Army Audiology and Speech Center (AASC) at Walter Reed Army Medical Center (WRAMC) evaluated more than 860 WIA service members from the Global War on Terrorism; of that number, 433-more than half-had blast-related injuries. These patients ranged in rank from private to colonel and were from all military services, although a majority was made up of Army and Marine personnel. With an age range of 18 to 58, the mean age of these patients was 28 years old. Of the blast-injured patients seen at AASC, 35% had traumatic injuries such as amputation or traumatic brain injury (TBI) with no apparent correlation between the prevalence or extent of polytrauma and any hearing loss or ear injury.

Speech-language pathologists at AASC evaluated more than 175 patients with blast injuries. Referrals for a large percentage of these patients were for swallowing evaluations (66%) and cognitive/linguistic deficits (56%). Other patients referred had tracheostomies requiring speaking valves (30%) and voice disorders (29%) (Newman, 2005).

During this same period audiologists at AASC evaluated 257 blast-injured patients, of which 64% had ear injury and hearing loss. Of those with otologic problems, 52% had sensorineural hearing loss, 21% had conductive hearing loss, and 27% had mixed hearing loss. Hearing loss was bilateral in 25% and unilateral in 34% of those with hearing loss. About 32% of these blast-injured patients had tympanic membrane perforation (Delaney, et al., in preparation).

Otologic Findings

The majority of WIA patients evacuated from the war with blast-related injuries require the services of surgeons (general surgery and neurosurgery) and orthopedics, accounting for 81% of the primary sites of injury and treating specialty. About 4% of all primary injuries require services of otolaryngology and audiology as the primary treating specialty. This is not to imply that patients with other injuries do not also have ear injuries, but only that ear injuries are not the primary injury.

The most common otologic finding in blast injury is tympanic membrane rupture, which will occur in 50% of adults at 5 lbs/in or about 185 dB peak pressure level (Kronenberg, et al., 1988; Zajtchuk and Phillips, 1989). The IEDs commonly employed by insurgents in Iraq produce pressures exceeding 60 lbs/in, reaching peak pressure in about 2.5 to 50 milliseconds (ms). Unsurprisingly, personnel who survive exposure to such blasts frequently suffer traumatic brain injury (TBI), traumatic amputation of limbs, and injury to the ear and multiple other organs.

A common problem at secondary and tertiary medical facilities treating complex polytrauma patients is that ear and balance deficits are often initially overlooked. Hearing loss can be misdiagnosed as unresponsiveness in cases of TBI. Patients with lower-limb amputations may have vestibular problems that are not readily identified. Long-term observation is important in all cases of blast injury to the ear due to potential latent sequelae. Postural instability and inner ear dysfunction may be evident up to six months post-blast trauma (Coen, 2002). Persistent tympanic membrane perforation can lead to formation of a cholesteatoma or other chronic middle ear pathology.

Team-Based Treatment

Ideally, secondary and tertiary medical management of blast-related injuries utilize an interdisciplinary team approach of all relevant disciplines and does not merely triage care by primary site of injury. Early identification and management of auditory and balance problems can expedite the return of injured service members to duty or a high functional level.

WRAMC is the primary military treatment facility in the United States that receives most of the WIA evacuated patients from the war in Iraq and Afghanistan. Interdisciplinary teams that have been successfully engaged in caring for these patients at WRAMC include:

  • Traumatic Brain Injury (TBI) Team-comprised of neurology, neuropsychology, social work, psychiatry, speech-language pathology, and audiology
  • Physical Medicine and Rehabilitation (PM&R) Team-comprised of physiatry, physical therapy, occupational therapy, psychiatry, social work, nutrition, speech-language pathology, and audiology

Audiologists and physical therapists tend to work closely together in treating blast-injured patients, since both disciplines are often the first to manage oto-vestibular and hearing impairments in blast injuries. Audiologists assess middle ear integrity and function, hearing status, and evaluate vestibular dysfunction. Physical therapists evaluate motor function, postural stability and gait, provide vestibular rehabilitation training, and provide therapy for amputees. Working together, these two disciplines have particularly enhanced care and expedited rehabilitation of patients with traumatic amputations of the lower limb).

Noise Exposure

Currently, hazardous noise exposure is the greatest that it has been in the U.S. military in over 35 years. The notion of 'hearing conservation' largely emerged from the military's recognition of noise as an occupational hazard that must be prevented. Since implementing a concerted hearing conservation program in the mid-1970s, the incidence of noise-induced hearing loss was greatly reduced across the U.S. military services.

Regrettably, this successful trend has reversed in recent years for a variety of reasons. In addition to the current combat operations in Iraq and Afghanistan, deployment missions over the past 10 years have transitioned the military from a largely garrison-based force to an expeditionary force. Concurrently, military transformation initiatives have significantly reduced the number of uniformed audiologists that provide hearing conservation services. The result is that noise-induced hearing loss is increasing across the military at an alarming rate. Impaired hearing acuity (hearing loss and tinnitus) is the second most common new disability award from the VA for former service members, with 76,836 new awards in 2004. The total increase in new compensation awards for hearing loss and tinnitus exceeds 168% between 2000 and 2004.

Although the survival rate from battle injuries in current combat operations is better than in previous conflicts, a higher proportion of those wounded (compared to previous wars) have TBI, amputations and other traumatic blast-related injuries. Given the young ages of most of these casualties (24 to 28 years), and the fact that many are 'citizen soldiers' (i.e., U.S. Army Reserve and National Guard), the impact of such a patient population will be a larger, long-term rehabilitation burden on the VA, military, and civilian healthcare facilities.

Another potential problem will be the surge in the number of patients requiring hearing services due to the increasing incidence of noise-induced hearing loss. Robust, healthy young adults are traumatically transformed into severely injured individuals in about 50 ms-about one-fifth the length of time of an eye blink. Unlike most deficits that recover or acquire some asymptotic stage of performance, sensorineural hearing loss will continually worsen over a lifetime.

The healthcare industry faces many challenges and opportunities in best serving these patients. Healthcare providers generally do not understand hearing loss from blast and acute acoustic trauma as a sensory deficit, and medical education is important to resolving this quandary. Advances in medical practice should be made to employ an interdisciplinary team approach to caring for patients with complex polytrauma. Emerging technologies and strategies for preventing and treating noise-induced hearing loss (e.g., pharmocologic agents, non-linear hearing protective devices) must continue to be developed and employed. Now more than ever, the audiology profession has the opportunity and responsibility to champion such efforts.

Col. David W. Chandler, is a colonel in the US Army and audiologist currently serving as director of the Department of Defense Executive Agencies Directorate at the Office of The Army Surgeon General, Washington, DC. He is the former director of the Army Audiology and Speech Center at Walter Reed Army Medical Cente. Contact him at David.Chandler@us.army.mil.

cite as: Chandler, C. W. (2006, July 11). Blast-Related Ear Injury in Current U.S. Military Operations : Role of Audiology on the Interdisciplinary Team. The ASHA Leader.

Army Study Probes Hearing Loss

A study by audiologist Thomas M. Helfer and others found significant higher rates of post-deployment noise-induced hearing loss injury among U.S. Army soldiers after exposure to combat-related noise than among soldiers who had not served in combat. Researchers found that soldiers sent to battle zones were 52.5 times more likely to suffer auditory damage.

The article, published in the December 2005 issue of the American Journal of Audiology (AJA) won a 2006 ASHA Editor's Award. To access the article, visit http://aja.asha.org/cgi/reprint/14/2/161.



References

Cohen J., Ziv, G., Bloom, J., Zikk, D., Rapoport, Y., & Himmelfarb, M. (2002). Blast injury of the ear in a confined space explosion: Auditory and vestibular evaluation. Israeli Journal of Military Medicine, 7, 559-562.

Delaney, K., Cornish, E., Chandler, D., & Walden, T. (2006). Blast injury of the ear: Clinical update from the global war on terror. Manuscript in preparation.

Kronenberg, J., Ben-Shoshan, J., Modan, M., & Leventon, G. (1988). Blast injury and cholesteatoma. American Journal of Otology, 9(2), 127-30.

Mudry, A. (1999). Contribution of Ambroise Pare (1510-1590) to otology. American Journal of Otology, 20(6), 809-813.

Newman, L. (2005). Communication of clinical report of data from Speech-Language Pathology, Army Audiology and Speech Center, Walter Reed Army Medical Center, 5 October.

Zajtchuk, J. T., & Phillips, Y. Y. (1989). Effects of blast overpressure on the ear. Annals of Otology, Rhinology, and Laryngology, 98 (Supplement 140), 5.



  

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