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Explosions and Blast Injuries

A Primer for Clinicians

Our courses fulfill continuing nursing education requirements in all 50 states. For more accreditation information, click here.

Unless otherwise cited, the material in this course was based on a report of the Centers for Disease Control and Prevention entitled Explosions and Blast Injuries: A Primer for Clinicians.

Learning objectives and post test by Lauren Robertson, BA, MPT, and Sharon Sanders, RN.

As the risk of terrorist attacks increases in the United States, disaster response personnel must understand the unique pathophysiology of injuries associated with explosions and be prepared to assess and treat the people injured by them. Bombs and explosions can cause unique patterns of injury seldom seen outside combat.

Penetrating injuries and blunt trauma predominate among survivors following an explosion. Blast lung is the most common fatal injury among initial survivors. Explosions in confined spaces (eg, mines, buildings, large vehicles) and/or structural collapse are associated with greater morbidity and mortality.

Half of all initial casualties will seek medical care over a one-hour period. This can be useful in predicting demand for care and resource needs. Expect an "upside-down" triage—the most severely injured arriving after the less injured, who bypass EMS triage and go directly to the closest hospital.

Explosions have the potential to inflict multi-system, life-threatening injuries on many persons simultaneously. The injury patterns following such events are a product of the composition and amount of materials involved, the surrounding environment, delivery method (if a bomb), the distance between the victim and the blast, and any intervening protective barriers or environmental hazards. Because explosions are relatively infrequent, blast-related injuries can present unique triage, diagnostic, and management challenges to providers of emergency care.

Few U.S. health professionals have experience with explosives-related injuries. Vietnam-era physicians are retiring, other armed conflicts have been short-lived, and until recently the United States was largely spared of the scourge of mega-terrorist attacks. In today's climate, with its emphasis on homeland security, it is appropriate that healthcare professionals expect the unexpected and review procedures for explosive and blast injuries.

CLASSIFICATION OF EXPLOSIVES

Explosives are categorized as high-order explosives (HE) or low-order explosives (LE).

High-order explosives produce a defining supersonic over-pressurization shock wave. Examples of HE include TNT, C-4, Semtex, nitroglycerin, dynamite, and ammonium nitrate fuel oil (ANFO).

Low-order explosives create a subsonic explosion and that does not produce over-pressurization. Examples of LE include pipe bombs, gunpowder, and most purely petroleum-based bombs such as Molotov cocktails or aircraft improvised as guided missiles. High-order and low-order explosives cause different injury patterns.

Explosive and incendiary (fire) bombs are further characterized based on their source.

Manufactured implies standard military-issued, mass-produced, and quality-tested weapons. Improvised describes weapons produced in small quantities, or the use of a device outside its intended purpose, such as converting a commercial aircraft into a guided missile.

Manufactured (military) explosive weapons are exclusively HE-based. Terrorists will use whatever is available—illegally obtained manufactured weapons or improvised explosive devices (IEDs) that may be composed of HE, LE, or both. Manufactured and improvised bombs cause markedly different injuries.

PREHOSPITAL MANAGEMENT

Initial triage, trauma resuscitation, and transport of patients follows standard protocols for multiple-injured patients or mass casualties. Explosions in confined spaces result in a higher incidence of primary blast injury, including blast lung injury. Note the patient's location and the surrounding environment at the time of injury (CDC, 2006).

Patients with suspected or confirmed blast lung injury (BLI, see discussion below) should receive supplemental high-flow oxygen to prevent hypoxemia. A compromised airway requires immediate intervention. If ventilatory failure is imminent, or occurs, patients should be intubated; however, prehospital providers must realize that mechanical ventilation and positive pressure may increase the risk of alveolar rupture, pneumothorax, and air embolism in BLI patients (CDC, 2006).

High-flow oxygen is administered if air embolism is suspected, and the patient is placed in a prone, semi–left lateral, or left-lateral position. Clinical evidence or suspicion of a hemothorax or pneumothorax warrants close observation. Chest decompression should be performed for patients clinically presenting with a tension pneumothorax. Close observation is imperative for any patient suspected of BLI who is transported by air (CDC, 2006).

Fluids are administered judiciously because overzealous fluid administration in the patient with BLI may result in volume overload and worsen pulmonary status. In accordance with community response plans for mass-casualty events, patients with BLI must be transported rapidly to the nearest appropriate facility (CDC, 2006).

BLAST INJURIES

Mechanisms of Injuries

The four basic mechanisms of blast injury are termed as primary, secondary, tertiary, and quaternary (Table 1). An example that causes primary injury is blast wave, which refers to the intense over-pressurization impulse created by a detonated HE. Blast injuries are characterized by anatomic and physiologic changes that occur when the direct or reflective over-pressurization force impacts the body's surface. The HE blast wave (over-pressure component) should be distinguished from blast wind (forced superheated air flow). Blast wind may be encountered with both HE and LE.

TABLE 1

MECHANISMS OF BLAST INJURY

Category	Characteristics	Body part	Affected types of injuries
Primary	Unique to high-order explosives; results from the impact of the overpressurization wave with body surfaces	Gas-filled structures are most susceptible: lungs, GI tract, middle ear
			Blast lung (pulmonary barotrauma)
			Tympanic membrane rupture and middle-ear damage
			Abdominal hemorrhage and perforation
			Globe (eye) rupture
			Concussion (traumatic brain injury without physical signs of head injury)
Secondary	Results from flying debris and bomb fragments	Any body part
			Penetrating ballistic (fragmentation) or blunt injuries
			Eye penetration (can be occult)
Tertiary	Results when bodies are thrown by blast wind	Any body part
			Fracture and traumatic amputation
			Closed and open brain injury
Quaternary	All explosion-related injuries, illnesses, or diseases not due to primary, secondary, or tertiary mechanisms; includes exacerbation or complications of existing conditions	Any body part
			Burns (flash, partial- and full-thickness)
			Crush injuries
			Closed and open brain injury
			Asthma, COPD, or other breathing problems from dust, smoke, or toxic fumes
			Angina
			Hyperglycemia, hypertension

Low-order explosives are classified differently because they lack the defining over-pressurization wave of HEs. Low-order explosives cause injury from ballistics (fragmentation), blast wind (not blast wave), and thermal. There is some overlap between LE descriptive mechanisms and HE's secondary, tertiary, and quaternary mechanisms.

TABLE 2

OVERVIEW OF EXPLOSIVE-RELATED INJURIES

System	Injury or condition
Auditory	Tympanic membrane (TM) rupture, ossicular disruption, cochlear damage, foreign body
Eye, orbit, face	Perforated globe, foreign body, air embolism, fractures
Respiratory	Blast lung, hemothorax, pneumothorax, pulmonary contusion and hemorrhage, A-V fistulas (source of air embolism), airway epithelial damage, aspiration pneumonitis, sepsis
Digestive	Bowel perforation, hemorrhage, ruptured liver or spleen, sepsis, mesenteric ischemia from air embolism
Circulatory	Cardiac contusion, myocardial infarction from air embolism, shock, vasovagal hypotension, peripheral vascular injury, air embolism–induced injury
CNS injury	Concussion, closed and open brain injury, stroke, spinal cord injury, air embolism–induced injury
Renal injury	Renal contusion, laceration, acute renal failure due to rhabdomyolysis, hypotension, and hypovolemia
Extremity injury	Traumatic amputation, fractures, crush injuries, compartment syndrome, burns, cuts, lacerations, acute arterial occlusion, air embolism–induced injury

Up to 10% of all blast survivors have significant eye injuries, generally due to perforations from high-velocity projectiles. They can occur with minimal initial discomfort, and present for care days, weeks, or months after the event. Symptoms include eye pain or irritation, foreign body sensation, altered vision, periorbital swelling, or contusions. Findings can include decreased visual acuity, hyphema, globe perforation, subconjunctival hemorrhage, foreign body, or lid lacerations. Liberal referral for ophthalmologic screening is encouraged.

Blast Lung Injury (BLI)

Blast lung injury (BLI) is a direct consequence of the high-order explosive over-pressurization wave. It is the most common fatal primary blast injury among initial survivors. Signs of blast lung are usually present at the time of initial evaluation, but they have been reported as late as 48 hours after the explosion. Blast lung is characterized by the clinical triad of apnea, bradycardia, and hypotension.

Pulmonary injuries vary from scattered petechiae to confluent hemorrhages. Blast lung should be suspected for anyone with dyspnea, cough, hemoptysis, or chest pain following a blast exposure. Blast lung produces a characteristic "butterfly" pattern on chest x-ray. A chest x-ray is recommended for all exposed persons and a prophylactic chest tube (thoracostomy) is recommended before general anesthesia or air transport if blast lung is suspected.

Figure 1     Serial x-ray from a blast injury November 11, 1943. (A) Twenty-four hours after the injury, showing haziness or cloudiness that indicates petechial pulmonary hemorrhage and edema. (B) Seven days after the injury, showing clearing of the lung fields. (C) Sixteen years after the injury, the only abnormality is slight emphysema.

Blast lung injury presents unique triage, diagnostic, and management challenges. It is a major cause of morbidity and mortality for blast victims both at the scene and among initial survivors. The blast wave's impact upon the lung results in tearing, hemorrhage, contusion, and edema with resultant ventilation-perfusion mismatch. Blast lung injury is a clinical diagnosis and is characterized by respiratory difficulty and hypoxia, which may occur without obvious external injury to the chest (CDC. 2003a).

CLINICAL PRESENTATION

Symptoms may include dyspnea, hemoptysis, cough, and chest pain. Signs may include tachypnea, hypoxia, cyanosis, apnea, wheezing, decreased breath sounds, and hemodynamic instability. Associated pathology may include bronchopleural fistula, air emboli, and hemothoraces or pneumothoraces. Other injuries may be present (CDC, 2003a).

DIAGNOSTIC EVALUATION

Chest radiography is necessary for anyone who is exposed to a blast. A characteristic butterfly pattern may be revealed upon x-ray. Arterial blood gases, computed tomography (CT scan), and Doppler technology may be needed. Most laboratory and diagnostic testing can be conducted per resuscitation protocols and further directed based upon the nature of the explosion (CDC. 2003a).

MANAGEMENT

Initial triage, trauma resuscitation, treatment, and transfer should follow standard protocols; however, some diagnostic or therapeutic options may be limited in a disaster or mass-casualty situation. In general, managing blast lung injury is similar to caring for pulmonary contusion, which requires judicious fluid use with administration ensuring tissue perfusion that avoids volume overload (CDC, 2003a).

CLINICAL INTERVENTIONS

All patients with suspected or confirmed blast lung injury should receive supplemental high-flow oxygen sufficient to prevent hypoxemia. Delivery may include nonrebreather masks, continuous positive airway pressure, or endotracheal intubation. Impending airway compromise, secondary edema, injury, or massive hemoptysis requires immediate intervention to secure the airway. Patients with massive hemoptysis or significant air leaks may benefit from selective bronchus intubation (CDC, 2003a).

Clinical evidence or suspicion of a hemothorax or pneumothorax warrants prompt decompression. If ventilatory failure is imminent, or occurs, patients should be intubated; however, caution must be used in the decision to intubate patients, as mechanical ventilation and positive end pressure may increase the risk of alveolar rupture and air embolism. High-flow oxygen should be administered if air embolism is suspected, and the patient should be placed in prone, semi–left lateral, or left-lateral positions. Patients treated for air emboli should be transferred to a hyperbaric chamber (CDC, 2003a).

DISPOSITION AND OUTCOME

There are no definitive guidelines for observation, admission, or discharge following emergency department evaluation for patients with possible BLI following an explosion.

Patients diagnosed with BLI may require complex management and should be admitted to an intensive-care unit. Patients with any complaints or findings suspicious for BLI should be observed in the hospital. Discharge decisions will also depend upon associated injuries and other issues related to the event, including the patient's current social situation (CDC, 2003a).

In general, patients with normal chest radiographs and arterial blood gas (ABGs) who have no complaints that would suggest BLI can be considered for discharge after 4 to 6 hours of observation. Data on the short- and long-term outcomes of patients with BLI is currently limited. However, in one study conducted on survivors one year post injury, no patients had pulmonary complaints, all had normal physical examinations and chest radiographs, and most had normal lung function tests (CDC, 2003a).

Other Injuries

EAR INJURY

Primary blast injuries of the auditory system are easily overlooked but they can cause significant morbidity. Injury is dependent on the orientation of the ear to the blast. Tympanic membrane (TM) perforation is the most common injury to the middle ear. Signs of ear injury are usually present at time of initial evaluation and should be suspected for anyone presenting with hearing loss, tinnitus, otalgia, vertigo, bleeding from the external canal, TM rupture, or mucopurulent otorrhea. All patients exposed to blast should have an otologic assessment and audiometry.

ABDOMINAL INJURY

Gas-containing sections of the gastrointestinal tract are most vulnerable to primary blast effect. This can cause immediate bowel perforation, hemorrhage (ranging from small petechiae to large hematomas), mesenteric shear injuries, solid organ lacerations, and testicular rupture. Blast abdominal injury should be suspected in anyone exposed to an explosion who has abdominal pain, nausea, vomiting, hematemesis, rectal pain, tenesmus, testicular pain, unexplained hypovolemia, or any findings suggestive of an acute abdomen. Clinical findings may be absent until the onset of complications.

BRAIN INJURY

Primary blast waves can cause concussions or mild traumatic brain injury (TBI) without a direct blow to the head. Consider the proximity of the victim to the blast, particularly when the patient complains of headache, fatigue, poor concentration, lethargy, depression, anxiety, insomnia, or other constitutional symptoms. The symptoms of concussion and post traumatic stress disorder can be similar.

The signs and symptoms of a TBI can be subtle. Symptoms of a TBI may not appear until days or weeks following the injury or may even be missed when patients appear fine, even though they may act or feel differently (CDC, 2005b).

Diagnosing a TBI is challenging because symptoms are often common to other medical conditions and the severity of the symptoms can change over time. Any patient may have a TBI who has a history of head trauma or who is suffering from confusion, disorientation, amnesia of events around the time of injury, loss of consciousness of 30 minutes or less, neurologic or neuropsychological problems, or who has a Glasgow Coma Scale (GCS) score of 13 or higher. Taking a careful medical history can be key to detecting a TBI. Any unusual or unexplained signs or symptoms should be evaluated further (CDC, 2005b).

EMERGENCY MANAGEMENT OPTIONS

Follow your hospital and regional disaster plan. Expect an upside-down triage, with the most severely injured arrive after the less injured, who typically bypass EMS triage and go directly to the closest hospitals.

Double the first hour's casualties for a rough prediction of the total first wave of casualties.

Obtain and record details about the nature of the explosion, potential toxic exposures and environmental hazards, and casualty location from police, fire, EMS, ICS commander, regional EMA, health department, and reliable news sources. If structural collapse occurs, expect increased severity and delayed arrival of casualties.

When trying to determine how many casualties a hospital can expect after a mass-casualty event, it is important to remember that casualties present quickly and that approximately half of all casualties will arrive at the hospital within a one-hour window. This one-hour window begins when the first casualty arrives at the hospital (CDC, 2003b).

The total expected number of casualties will be an estimate. There are many factors that may affect the accuracy of this prediction, including transportation difficulties and delays, security issues that may hinder access to victims, and multiple explosions or secondary effects of explosion (such as a building collapse) (CDC, 2003b).

PATTERNS OF HOSPITAL USE

In the confusion that often follows a mass-casualty event, managing a hospital can be challenging. Historically, mass-casualty events show patterns of hospital use. Public health professionals and hospital administrators can use this information to handle resource and staffing issues during a mass-casualty event (CDC, 2003b).

Within ninety minutes following an event, 50% to 80% of the acute casualties will likely arrive at the closest medical facilities. Other hospitals outside the area usually receive few or no casualties. The less-injured casualties often leave the scene under their own power and go to the nearest hospital. As a result:

• They are not triaged at the scene by emergency medical services (EMS).
• They may arrive to the hospital before the most injured.
• On average, it takes 3–6 hours for casualties to be treated in the emergency department (ED) before they are admitted to the hospital or released (CDC, 2003b).

MEDICAL MANAGEMENT OPTIONS

Blast injuries are not confined to the battlefield. They should be considered for any victim exposed to an explosive force. Clinical signs of blast-related abdominal injuries may be silent initially until signs of acute abdomen or sepsis come forward. Standard penetrating and blunt trauma to any body surface are the most common injuries seen among survivors.

Primary blast lung and blast abdomen are associated with a high mortality rate. Blast lung is the most common fatal injury among initial survivors. Blast lung presents soon after exposure. It can be confirmed by finding a butterfly pattern on chest x-ray. Prophylactic chest tubes (thoracostomy) are recommended when general anesthesia and/or air transport are likely.

Auditory system injuries and concussions are easily overlooked. The symptoms of mild traumatic brain injury and post traumatic stress disorder can be identical.

Isolated tympanic membrane rupture is not a marker of morbidity; however, traumatic amputation of any limb is a marker for multi-system injuries.

Air embolism is common, and can present as stroke, myocardial infarction, acute abdomen, blindness, deafness, spinal cord injury, or claudication. Hyperbaric oxygen therapy may be effective in some cases.

Compartment syndrome, rhabdomyolysis, and acute renal failure are associated with structural collapse, prolonged extrication, severe burns, and some poisonings. Consider the possibility of exposure to inhaled toxins and poisonings (eg, carbon monoxide, CN, MetHgb) in both industrial and criminal explosions.

Wounds can be grossly contaminated. Consider delayed primary closure and assess tetanus status. Ensure close follow-up of wounds, head injuries, eye, ear, and stress-related complaints. Communications and instructions may need to be written because of tinnitus and sudden temporary or permanent deafness.

Posted May 5, 2006

Expires February 2, 2009

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