Special Considerations for Military Personnel: Unique Aspects of Blast Injury

Michael S. Jaffee

OVERVIEW

Over the past decade, there has been increased attention and awareness regarding concussions and traumatic brain injury (TBI) and the associated comorbidities in our service members and veterans. The increase in the use of improvised explosive devices (IEDs) combined with use of body armor, which increases survival after significant injury, has led to TBI being referred to as a “signature injury of the war” [1]. A variety of programs to enhance detection and better standardize quality of care in a multidisciplinary fashion have emerged from this recognition. Although blast is an important component of combat injury, these treatments also benefit service members with noncombat concussions and TBIs.

DEFINITION

To standardize definitions and terminology, the Department of Defense (DoD) uses the following definition and classification system for mild TBI (MTBI) (concussion) and moderate-to-severe TBI.

The DoD definition is consistent with the definitions used by Centers for Disease Control (CDC), American Congress of Rehabilitation Medicine (ACRM), and World Health Organization (WHO).

Of note, loss of consciousness (LOC) is not required for a diagnosis, and the presence of symptoms alone without a known injury does not qualify for a diagnosis. The designation “complicated MTBI” or clinical presentation of MTBI but with abnormal imaging is not part of the DoD system of definition.

Mild	Moderate	Severe
Normal imaging	Normal or abnormal imaging	Abnormal imaging
Loss of Consciousness (LOC):0–30 min	LOC > 30 min < 24 hr	LOC > 24 hr
Alteration of Consciousness (AOC): up to 24 hr	AOC > 24 hr
Posttraumatic Amnesia (PTA):0–1 day	PTA > 1 and < 7 days	PTA > 7 days

EPIDEMIOLOGY

• From 2000 through the 3rd quarter of 2015, a total of 339,462 cases have been identified [2].

• Systematic screening programs began in 2007, increasing the yield.

• The largest annual incidence was in 2011 with 32,907 cases identified.

• The vast majority (82.4%) of cases identified are MTBI (i.e., concussion).

MECHANISMS

• The majority of DoD concussions and TBIs occur in a nondeployed setting and include training accidents, athletic concussions, and motor vehicle crashes (MVCs).

• Combat injuries may include blast as a component of injury.

• Of note: blast injuries often have an additional mechanism such as rollover or impact (i.e., more than a single mechanism, or “blast plus”).

BLAST WAVE PHYSICS

Explosive blasts produce transient pressure waves, which can reach the speed of sound [3]. This is characterized by an initial high pressure wave followed by a protracted low pressure wave. This has been well studied and known to affect fluid- and air-filled structures (e.g., eyes, ears, lungs, and gastrointestinal tract). Blast waves also may include heat and electromagnetic waves, which can further disrupt metabolic process and injure tissue.

MECHANISMS OF TBI WITH BLAST COMPONENT

Blast waves can cause TBI by several different commonly accepted mechanisms [4–15]. Primary, secondary, and quaternary mechanisms are generally considered unique to blast injury. The tertiary mechanism is akin to traditional closed head injuries.

• Primary injury represents the transduction of the blast wave itself, which can disrupt tissues. Understanding of the direct effect upon the brain is incomplete. It is unclear if the direct effect of the blast wave differs from more traditional causes of TBI in pathophysiology, neurological damage, or upon recovery patterns [16]. The three prevailing theories developed from animal models include:

Transduction of blast wave through skull causing biochemical dysfunction.

Vascular congestion from thorax injury causing transient pressure oscillations in the brain [17].

Retrograde cerebrospinal fluid pressure from compression in the spinal column causing increased pressure in the cranial cavity.

• Secondary injury signifies the damage caused by objects traveling at high rates of speed and striking the victim. TBI can be caused by:

Penetrating head injury due to shrapnel or other foreign bodies.

Traditional closed head injury patterns with focal contusions and diffuse axonal injury due to rapid acceleration and deceleration.

• Tertiary injuries occur when the individual is thrown from high rates of speed and strike stationary objects. TBI is caused by traditional closed head injury mechanics such as rapid acceleration and deceleration in multiple planes.

• Quaternary injuries represent effects from thermal and inhalation injuries. Brain injury is thought to be caused by hypoxic or toxic effects upon cerebral tissue.

COMORBIDITIES AND COMPLICATIONS

A. Psychological
Patients with a TBI sustained in combat have an increased risk for having psychological symptoms, including posttraumatic stress. Data show that up to 40% to 45% of combat injuries may have this comorbidity [18].

B. Polytrauma
Dual sensory impairment with involvement of both visual and auditory function in association with an MTBI can occur, due to both peripheral and central etiologies.

1. More than 60% of veterans of Operation Iraqi Freedom with histories of blast-related MTBI were found to have some degree of sensorineural hearing loss [19].

2. The presence of central auditory processing impairments appears to be common in soldiers with blast exposure, although the underlying cause is unknown.

3. Research on veterans with blast-related and other forms of TBI found that, in patients with moderate or severe TBI, 38.2% experienced an associated ocular injury. Reduced visual acuity was found in 16.7%, whereas 32.2% had visual field defects [20].

4. Special expertise in auditory and visual rehabilitation is necessary for the complete rehabilitation approach to blast-injured military personnel [17].

C. Vascular Complications
An additional risk identified with moderate-to-severe blast injuries is the increased risk of vascular injuries and complications, such as traumatic aneurysm, dissections, and vascular fistulae. In those with traumatic aneurysms, almost half developed vasospasm [21]. (See also Chapter 57 for a more detailed discussion of vascular complications associated with TBI.)

SCREENING IN DEPLOYED SETTING

(Identifies those who are experiencing symptoms possibly related to TBI; does not qualify as an official diagnosis.)

In 2010, collaboration between the medical corps and the Joint Chiefs of Staff led to new policy for the DoD, DTM-xxxx09-033. Rather than relying on a service member to self-report symptoms, any and all service members involved in certain situations at risk for concussion are to undergo a screening evaluation and a mandatory 24-hour rest period.

These situations include:

• Everyone involved in a vehicle associated with a blast event, collision, or rollover.

• Presence within 50 m of a blast (inside or outside).

• A direct blow to the head or witnessed LOC.

• Exposure to more than one blast event (the service member’s commander shall direct a medical evaluation).

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