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Injuries from explosives
Explosives have been used in every major conflict in which the United States has been involved and today are the primary mechanism of injury among U.S. combatants ( Fig. 1 ). Explosives, most notably improvised explosive devices (IEDs), are also commonly used against civilian targets. After a bomb attack on civilian populations, scene responders are responsible for triage and transport decisions, and then hospital personnel must retriage and reassess all patients who arrive at their facility. Most blast events are mass casualty incidents, and early recognition of symptoms that can point to more significant injury, within the chaos of the patient surge, is key to optimizing patient outcomes.
Mechanism of injury and lethality of explosion and gunshot wounds among U.S. forces from the Civil War to current conflicts. OEF, Operation Enduring Freedom (Afghanistan); OIF, Operation Iraqi Freedom (Iraq).
(Data from Bellamy RF, Zajtchuk R: Assessing the effectiveness of conventional weapons. In Conventional warfare: ballistic, blast, and burn injuries . Washington, D.C.: Office of the Surgeon General, 1991, pp 53–82; Beebe GW, DeBakey ME: Death from wounding. In Battle casualties, Springfield, IL, Charles C Thomas, 1952, pp 74–147; Reister FA: Battle casualties and medical statistics: U.S. Army experience in the Korean war. Washington, D.C.: The Surgeon General, Department of the Army, 1973; Hardaway RM: Viet Nam wound analysis. J Trauma 18:635–643, 1978; Global War on Terrorism by Reason, October 7, 2001 through April 4, 2011; Gawande A: Casualties of war—military care for the wounded from Iraq and Afghanistan. N Engl J Med 351:2471–2475, 2004.)
Incidence
Explosive devices are the most frequently used weapons in combat and by terrorists. In Afghanistan and Iraq, three fourths of the almost 50,000 injuries and deaths among U.S. troops were caused by explosive devices, often IEDs. *
* Data from October 7, 2001 through April 4, 2011. The category of explosion in this military data set encompasses the following: weaponry, artillery/mortar/rocket; weaponry, explosive device; weaponry, grenade; and weaponry, rocket-propelled grenade. “Weaponry, explosive device” is by far the largest category, encompassing 86% of the explosion-related injuries and deaths.
Among civilians throughout the world, 62% of the close to half million injuries and deaths (317,029 and 157,023, respectively) that occurred in the 77,134 terrorist attacks between January 1990 and April 2011 were caused by explosives. †
† The category of explosion in this civilian data set encompasses the following: arson/firebombing, bombing, and suicide. The category of “bombing” encompasses almost 70% of the explosion-related injuries and deaths.
Mechanisms of injury and diagnosis
A bomb is any container filled with explosive material whose explosion is triggered by a clock or other device. Bombs used by terrorists are primarily IEDs, may use a number of designs or explosives, and are of two types: (1) conventional (filled with chemical explosives containing hydrogen, oxygen, nitrogen, and carbon) or (2) dispersive (filled with chemicals or projectiles such as nails, steel pellets, screws, and nuts). Nuclear devices (outside the scope of this chapter) rely on nuclear fission or fusion. The term “blast injury” refers to the biophysical and pathophysiologic events and the clinical syndromes that occur when a living body is exposed to blast of any origin.
Blast injuries are unique in that they combine several mechanisms of injury including blunt, penetrating, and thermal. Therefore, knowledge of the mechanisms of blast effect and early recognition of the potential injuries are of paramount importance in the management of blast-injured patients. Blast injuries are classified according to their underlying mechanisms into five categories ( Table 1 ).
TABLE 1
Explosive Blast: Chain of Interactions and Injuries, Taxonomy, Typical Injuries, and Affected Body Regions
Data from Federal Emergency Management Agency: Explosive blast. In Primer to design safe schools projects in case of terrorist attacks , Washington, D.C.: Federal Emergency Management Agency, 2003, 4-1–4-13; Department of Defense Directive: Medical research for prevention, mitigation, and treatment of blast injuries. Number 6025.21E. July 5, 2006 (Defense Technical Information Center website). DePalma RG, Burris DG, Champion HR, et al: Blast injuries. N Engl J Med 352:1335–1342, 2005; Explosions and blast injuries: a primer for clinicians. CDC Mass Casualties. Reviewed June 14, 2006.
| Blast Interactions | Taxonomy of Injury | Typical Injuries |
|---|---|---|
| Detonation ↓ Shock front of blast wave created ↓ Shock front dissipates ↓ Blast wind ↓ Blast wind propels fragments, objects, people ↓ Heat, flames, gas, smoke generated; release of bacteria or radiation also possible |
Primary | |
| Injury produced by pressure differential causing direct tissue damage | Primarily organs with density interfaces, e.g., tympanic membrane rupture, blast lung, eye injuries, abdominal hemorrhage, concussion; can also rip through tissue and limbs | |
| Secondary | ||
| Injury produced by primary fragments from the exploding device (casing, items packed into the device) and secondary fragments (projectiles from the environment such as debris, glass, vehicular metal, etc.) | Any/all body regions Penetrating injuries, traumatic amputations, ocular injuries, lacerations, concussion Multiple injuries, most frequent type of injury | |
| Tertiary | ||
| Injury produced by the blast wave propelling individuals into hard objects or hard objects onto individuals; includes injuries caused by structural damage to and collapse of buildings | Any/all body regions Blunt injuries, crush and compartment syndrome, fractures, traumatic avulsions and amputations, brain injuries, concussion | |
| Quaternary | ||
| Injuries produced by other effects of explosions including heat, toxic gases, and environmental contamination | Any/all body regions Burns, inhalation injury, injury from environmental contamination, asphyxiation | |
| Quinary | ||
| Injuries produced by elements added to explosive devices such as radiation or bacteria; includes disease transmission from propelled biologic material such as bone fragments | Any/all body regions Radiation sickness, increased risk of disease | |
Primary blast injury
Primary blast injury results from the effects of pressure differentials (alternating over- and underpressure). Most vulnerable to primary blast injury are organs with density interfaces, namely the ear, lung, and gastrointestinal (GI) tract; effects of a range of pressures are shown in Table 2 .
TABLE 2
Short-Duration Pressure Effects Upon Unprotected Persons
| Pressure (Pounds per Square Inch) | Effect |
|---|---|
| 5 | Possible eardrum rupture |
| 15 | 50% chance of eardrum rupture |
| 30−40 | Slight chance of lung injury |
| 80 | 50% chance of lung injury |
| 100−200 | Slight chance of death |
| 130−180 | 50% chance of death |
| 200−250 | Almost certain death |
Diagnosis and management
Patients are at greater risk for primary blast injury when they are close to the point of detonation, are in an enclosed space (regardless of whether the explosion occurred inside or outside the enclosure), or are near a solid surface such as a wall that reflects and amplifies the blast wave. The diagnosis of primary blast injury is complicated by the fact that it can occur with little or no outward signs of injury and that symptoms may not be immediately apparent.
Ears
Ear injury may be suspected when there is bleeding or discharge from the ear; earache; tinnitus; vertigo; or immediate, sometimes transient, loss of hearing. Tympanic membrane rupture is the most common injury to the ear, but high overpressure may cause more significant injury such as dislocation and fracture of the ossicles, cochlear damage, and traumatic disruption of the oval or round window and subsequent permanent hearing loss. The Centers for Disease Control and Prevention (CDC) recommends that patients who have been exposed to an explosive blast receive an otologic assessment and audiometry.
The facts that tympanic membrane injury occurs at low pressure and that much more pressure is needed to damage other structures has suggested that tympanic membrane perforation is an indicator of primary blast injury. Recent research, however, has shown tympanic membrane perforation to be an unreliable indicator; thus, all victims of explosions should be assessed for primary blast injury regardless of whether their tympanic membranes are perforated.
In treating tympanic membrane rupture, foreign bodies should not be removed from the ear, nor should water or other nonsterile substances be introduced. Neither prophylactic antibiotics nor otologic suspensions should be introduced, but ophthalmologic gentamicin may be used. Treatment primarily consists of pain management and subsequent referral to an ear, nose, and throat specialist if significant debris is present or if symptoms persist.
Lungs
Primary blast injury to the lung (commonly known as “blast lung”) occurs at air pressures of approximately 56 to 76 pounds per square inch. It is sometimes accompanied by a clinical triad of apnea, bradycardia, and hypotension. Signs and symptoms may be evident upon presentation or may manifest as late as 48 hours from the time of the initial incident. Insidious characteristics of blast lung injury include the fact that initial signs and symptoms are easily underestimated, or missed, and that the patient’s condition may deteriorate rapidly to the point of needing mechanical ventilation. Warning signs for clinicians may be grouped into the categories of hemorrhage or escape of air. Nonspecific symptoms common to primary blast injury include chest pain and dyspnea, confirmed on examination by the presence of cyanosis and tachypnea.
The CDC recommends that anyone exposed to explosive blast be given a chest radiograph to rule out blast lung, which may be identified by a characteristic “butterfly” pattern. Computed tomography and Doppler scanning and arterial blood gas analysis may also be used to help make the diagnosis if they do not delay treatment. When blast lung is suspected, the CDC also recommends tube thoracostomy prior to air evacuation or administration of general anesthesia.
Management of blast lung injury is similar to that for pulmonary contusion. Treatment options include administration of fluid (without volume overload) and high-flow oxygen, treatment for airway compromise if needed, prompt decompression when evidence indicates hemothorax or pneumothorax, and intubation (being careful to avoid alveolar rupture and air embolism).
Abdomen
Primary blast injury to the abdomen is highly lethal and may have few initial signs. Clinical examination may reveal peritonitis, absent bowel sounds, shock, abdominal tenderness, and ensuing sepsis. Immediate injuries may include mesenteric shear injuries, solid organ lacerations, testicular rupture, hemorrhage (hematoma and subsequent obstruction, GI bleeding, hemoperitoneum), or escape of contents (mediastinitis, peritonitis). Symptoms may include abdominal, rectal, or testicular pain; nausea; vomiting; hematemesis; tenesmus; unexplained hypovolemia; or any indications of acute abdomen. Perforation of the bowel may be immediately apparent or may not be evident for hours. Insidious manifestations of symptoms and the presence of additional life-threatening injuries often make abdominal injury difficult to recognize; thus, repeated clinical examination is warranted.
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