Page 106 - 2020 JSOM Winter

The Downrange Acoustic Toolbox

An Active Solution for Combat-Related Acute Acoustic Trauma

1
2
3
J.D.E. Lee, MB, ChB ; D.M. Bowley, QHS FRCS ; J.A. Miles, MB, ChB, MRCGP ;
J. Muzaffar, MSc FRCS(ORL-HNS) ; R. Poole, MBBS, MRCGP ;
4
5
L.E. Orr, DM FRCS, FRCS(ORL-HNS) *
6

ABSTRACT
Frontline military personnel are at high risk of acute acoustic amounts, and factors such as the rate of pressure rise play a
trauma (AAT) caused by impulse noise, such as weapon firing considerable role. Unprotected exposure to a short impulse
6
or blast. This can result in anatomic disruption of the tympanic sound (±overpressure), typically peaking at or over 100dB
membrane and damage to the middle and inner ear, leading (e.g., explosion, firing of a weapon), usually results in acute
to conductive, sensorineural, or mixed hearing loss that may acoustic trauma (AAT), and this in turn can lead to acute, sen-
be temporary or permanent. AAT reduces warfighters’ opera- sorineural noise–induced hearing loss (NIHL). In 1950, Ben-
tional effectiveness and has implications for future quality of zinger described the blast wave as a “shot without a bullet, a
7
life. Hearing protection devices can mitigate AAT but are not slash without a sword” and, in reference to AAT, this contin-
completely protective. Novel therapeutic options now exist; ues to be an apt description. The current proposed mechanism
therefore, identification of AAT as soon as possible from point resulting in hearing loss from AAT is thought to be damage
of injury is vital to ensure optimal treatment and fulfillment of caused by blast overpressure as a result of direct mechanical
the duty of care. Early recognition and treatment of frontline insult, metabolic disturbances leading to cell death, or a com-
AAT can maintain the deployed team’s capabilities, avoid un- bination of both. Prolonged exposure to a loud sound above
necessary case evacuation (CASEVAC), and raise awareness 85dB (e.g., concert musicians) can cause chronic NIHL.
8,9
of military occupational AAT. This will help prioritize hearing Different exposure profiles can produce differing injury pat-
preservation, maintain the fighting force, and ultimately retain terns. Ninety percent of those hospitalized because of injuries
personnel in service. The UK Defence hearWELL research col- sustained in the Boston marathon bombing (2013) suffered
laboration has developed a frontline protocol for the assess- perforated TMs ; fewer otologic sequalae were noted in those
10
ment of AAT utilizing future-facing technology developed by injured during the Manchester Arena bombing (2017).
the US Department of Defense: the Downrange Acoustic Tool-
box (DAT). The DAT has been operationally deployed since It is important to distinguish AAT from other types of hearing
2019 and has successfully identified AAT requiring treatment, loss and accurately assess the degree to which it is sensori-
thereby improving casualties’ hearing and reducing unneces- neural in nature because two factors are paramount for mini-
sary repatriation. mizing the long-term sequalae: (1) early identification through
10
comprehensive audiologic assessment and (2) timely rescue
Keywords: hearing loss, noise-induced; acute acoustic treatment. 11
trauma; noise, occupational; military personnel; hearing pro-
tective devices; telemedicine; steroid Service personnel (SP) are at high risk of AAT when deployed
on active duty, and this is likely to be the time when opera-
tional considerations make clinical assessment and treatment
most challenging. Using boothless audiometry technology
Introduction spearheaded by the US Department of Defense (DoD) Hear-
Excessive noise exposure leads to hearing loss that may be con- ing Center of Excellence, the UK Defence hearWELL Research
1
ductive, sensorineural, or mixed, temporary or permanent. Collaboration has developed an innovative project coined
The World Health Organization estimates that, worldwide, the DAT. The DAT aims to address this disparity by allow-
1.1 billion people aged 12 to 35 years are at risk of hearing ing downrange objective, comprehensive otologic/audiologic
1,2
loss secondary to recreational noise exposure. In the United assessment to support stratification of patients for hearing res-
Kingdom alone, an estimated 23,000 workers, 2800 members cue treatment and to reduce the impact of AAT on the military
3
of the Armed Forces, and 300,000 Armed Forces veterans population.

4
5
have occupational hearing problems. Conductive hearing loss
may result from blood or debris within the ear canal, tym- The relationship between noise and hearing loss in the military
panic membrane (TM) rupture, or ossicular chain disruption. was recognized around 500 years ago when Ambroise Paré,
The threshold of TM rupture is approximately 37kPa/185dB the French war surgeon, noted his patients suffered hearing
12
of sound pressure level; however, it can withstand much larger loss as a result of weapon firing. In 1782, Admiral Rodney of
*Correspondence to linda.orr@uhb.nhs.uk
2
1 Dr Lee is affiliated with University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK. COL Bowley is affiliated with the Royal
3
4
Centre for Defence Medicine, Birmingham. MAJ Miles is affiliated with the Medical Support Unit, Hereford, UK. Dr Muzaffar is a research
5
6
fellow, Royal Centre for Defence Medicine and University of Cambridge, Cambridge, UK. LTC Poole is affiliated with MAB, UK. LTC Orr is
affiliated with the Royal Centre for Defence Medicine, Birmingham.
104