Blast Injuries

Etiology

Explosives are classified as high- or low-order explosives. High-order explosives have a strong supersonic pressure wave, known as the blast wave or shock wave. Low-order explosions are subsonic and lack the high-order blast wave. Examples of low-order explosives include pipe bombs, gunpowder, and petroleum-based bombs. In addition to the blast wave, an explosion can cause blast wind. Blast wind is the flow of superheated air that can interact with people and objects and cause injury or damage.

Chemical explosions cause injuries in 4 categories (primary, secondary, tertiary, and quaternary). The 4 categories are based on the impact on the human body from the blast wave, blast wind, and environmental/material factors in the blast area. Immediate death can occur from an explosion as a result of extensive pulmonary injury with pulmonary hemorrhage, causing suffocation. A pulmonary air embolism, severe head injury, significant internal injury, amputation, or impalement on an object can also cause immediate death. The patient's clinical outcome determines the treatment strategy for patients with blast injuries.[5][6][7] 

Epidemiology

Blast injuries occur on various scales. In 2014, it was estimated that there were over 10,000 blast injuries related to fireworks in the United States. The Federal Bureau of Investigation reported that from 1987 to 1997, over 4000 injuries and 448 deaths occurred in the United States due to illegal explosions of bombs or incendiary devices. In 2013, a notable explosion occurred at a fertilizer plant in Texas, resulting in 15 deaths and many injuries. On a global scale, explosive devices are used as a means of terrorism. Blast injuries caused many of the injuries to military and civilian personnel in recent wars and conflicts.

Pathophysiology

Blast injuries are classified according to their cause. A blast injury is the direct result of the interaction with the energy released when matter is transformed into a gaseous state, which is emitted in various forms (heat, light, sound, and pressure waves).

Primary Blast Injury

Primary blast injury is caused by the blast wave moving through the body. Since only high-order explosives create a blast wave, primary blast injuries are unique to high-order explosions. The blast wave causes more extensive damage to air-filled organs. The resulting barotrauma can affect the lungs, auditory organs, the eye, brain, and gastrointestinal tract.

• Blast ear
  • Tympanic membrane rupture and middle ear damage
• Blast lung
  • Injury to the lung parenchyma
  • Can have delayed symptom presentation
• Blast brain
  • Injury to the brain parenchyma, even without direct injury to the head
• Blast eye
  • Rupture of the globe of the eye
• Blast belly
  • Injury causing abdominal hemorrhage and perforation (immediate and delayed), as well as injury to solid organs and testicular rupture

Primary blast injuries can be subtle and have a delayed presentation. Blast lung should be considered in any victim who has dyspnea, cough, hemoptysis, and/or chest pain. The respiratory system can sustain significant injury from a blast wave. If the pressure exceeds 40 psi, the victim could sustain a pulmonary contusion, pneumothorax, air embolism, interstitial parenchyma damage, and/or subcutaneous emphysema.

Pulmonary contusion is the most common respiratory injury and can present up to 48 hours after injury. Lung overstretch can also activate the vagus nerve, leading to apnea and/or bradycardia. Blast ear should be considered in any victim who has decreased hearing or hearing loss, tinnitus, vertigo, and/or bleeding from the ear. If there is bleeding from the ear, consider that the blast was intense enough to cause injury to the lungs and hollow organs. In instances when the ear is over-pressurized (greater than 5 psi), the bony ossicles of the ear can be dislocated, fractured, and /or permanently destroyed.[8] 

Blast belly should be considered in any victim presenting with abdominal pain, nausea, vomiting, vomiting blood, rectal pain, testicular pain, unexplained hypovolemia, abdominal distention, and/or rigidity. The colon is the most common area of hemorrhage and perforation. As with blast lung, intestinal perforation may occur acutely or present with a delayed onset of up to 48 hours. Solid internal abdominal organs can also be contused or lacerated; however, solid organ damage occurs much less than does hollow organ damage.

Blast brain should be considered in any victim presenting with headache, fatigue, confusion, poor concentration, amnesia, decreased level of consciousness, depression, anxiety, and/or insomnia. Blast eye should be considered in victims with eye pain, swelling, contusion or ecchymosis around the orbit, bleeding from the eye, decreased vision, and/or blindness.[9] The blast wave may also damage the heart. Victims can have chest pain, tachycardia, decreased pulse pressure, cardiac dysrhythmias, and/or hypotension as a result of heart involvement. In victims with multiple presenting injuries or in incidents with multiple casualties, injuries could be easy to miss. Victims of primary blast injuries may not initially show any obvious signs of injury.  

Secondary Blast Injury

Secondary blast injuries are caused by debris that is displaced by the blast wind of the explosion, and this debris may penetrate or interact with the body surface. The debris can be from pieces of the explosive device itself or material located around the initial blast device at the time of the explosion. Secondary blast injuries account for the majority of injuries from an explosion event. The blast wave can carry debris a considerable distance, causing injuries to anyone in its path. Intentional explosive devices are often constructed with the intent to injure as many people as possible. The device could be built with nails, metal ball bearings, screws, or other objects that are forcefully displaced during the blast, causing additional injuries to anyone in the vicinity of the explosion.

Secondary blast injuries are the most common cause of mortality in victims of an explosion. Exposed areas of the victims’ bodies are at high risk for penetration of debris that is propelled by the explosion. The head, neck, and extremities are the areas at highest risk for injury. Secondary blast injuries are often apparent but can be deceiving. The force of the explosion can propel debris many times faster than a bullet. Thus, a seemingly minor wound could hide a devastating injury beneath. Injuries can include fractures, amputations, lacerations, dislocations, and soft-tissue injuries.[3]

Tertiary Blast Injury

Tertiary blast injuries are caused when the force of the blast wind propels the victim. Injuries are determined by what the victim strikes. The resulting injury can be either blunt trauma or penetrating injury, and the strength of the explosion determines the severity of the injuries sustained. Tertiary blast injury may comprise, but is not limited to, traumatic brain injury, fractured bones, soft tissue damage, solid organ injury, hollow viscus injury, and spinal injury. Injuries may be similar to severe blunt trauma from a motor vehicle collision or a high fall. Treatment depends on the identified injuries.[10][11]

Quaternary Blast Injury

Quaternary blast injuries are comprised of all injuries that are not included in primary, secondary, or tertiary blast injury categories. Quaternary blast injuries can result from exposure to fire, fumes, radiation, biological agents, smoke, dust, toxins, and environmental factors, as well as the psychological impact of the event. Due to the debris, wounds can become extremely contaminated from a wide variety of sources.[12]

• Fire: burn injuries (flash, partial, full-thickness, airway)
• Fumes/smoke/dust: inhalation injuries resulting in respiratory compromise
• Toxins: toxidromes from chemical exposures
• Environmental: heat/cold, exposure injuries
• Radiation: minor injury to death, depending on the type, amount, and exposure time to the source
• Biological: a variety of illnesses related to the agent released

A victim’s underlying medical condition has a major impact on the effects of the resulting exposure on their mortality and morbidity:

• Lung disease: exacerbation of chronic obstructive pulmonary disease or asthma
• Heart disease: unstable angina, acute myocardial infarction
• High blood pressure: hypertensive emergency or urgency
• Psychological disease: exacerbation of anxiety and/or depression; contributes to post-traumatic stress disorder

In an intentional explosion, other substances can be added to cause greater injury or illness, or to induce greater fear and panic in the community.[8][11]

Quinary Blast Injuries

Quinary injuries (hyperinflammatory or toxic additive exposures) may present with unexplained hypotension, altered mental status, or systemic inflammatory response out of proportion to visible trauma.

Histopathology

Several tissue and cell models have been created to study the effects of blast injury on tissue and cellular processes. The nervous system is of special interest to researchers, as the long-term effects of blast injury on neurons and subsequent clinical sequelae are not well understood. In vitro cell models using human neuroblastoma cells have shown significant effects on the cells when exposed to a shock wave.

There is a decrease in adenosine triphosphate levels, accompanied by increases in lactate and reactive oxygen species; further studies are needed to understand the clinical effects of these changes. Additional emerging research suggests that induced human pluripotent stem cell-derived brain organoids may serve as an alternative to animal models for studying the effects of blast waves on brain cells. Advancements in artificial intelligence modeling show promise for understanding the negative effects of blast injuries at the cellular level.[13][14][15]

Toxicokinetics

Toxicokinetics will be determined by the other substances or toxins released during the explosion. Blast injuries often involve debris that is embedded inside the patient. If not removed, it can cause serious long-term adverse effects. Prolonged exposure to toxic heavy metals leads to deleterious health outcomes, including brain damage and kidney injury. Retained metal fragments from blast debris can lead to toxic metal exposure. The toxic metal can lead to permanent damage to organs, such as the kidneys.[16]

History and Physical

A history and physical examination are required to determine the extent of injuries. This should take place in a location that is marked as safe. The location of the victim in proximity to the explosion, the surrounding infrastructure, nearby chemicals, and the potential number of other victims can aid in diagnosing the extent of injuries. A determination of the victim's disability and the events leading to the incident can help guide the need for further evaluation and treatment.

Evaluation

The evaluation should begin with the Advanced Trauma Life Support primary survey. The primary survey starts with control of exsanguinating hemorrhage before moving to evaluation of the airway, breathing, circulation, disability, and exposure. Once the primary survey is complete, the secondary head-to-toe survey is completed to evaluate for other injuries. The nature of the injuries will dictate what imaging and laboratory studies should be obtained.

The blast wave can transmit energy that results in inconspicuous external damage but severe internal injuries to the victim. Consequently, there should be a high index of suspicion for internal injuries when determining additional studies. Imaging studies may include x-rays, ultrasound, computed tomography scans, and magnetic resonance imaging. Laboratory studies may include venous and arterial blood gases, complete metabolic panel, complete blood count, lactate, lipase, coagulation panel, and toxin assays.[13]

Treatment / Management

Treatment and management are dictated by the injuries identified on primary and secondary surveys, along with any imaging studies performed. Careful review and evaluation for blast injuries that can present in a delayed fashion need to be specifically ruled out, if indicated. Treatment of injuries can be broken down into stages: preparation, resuscitation, consideration of antibiotics, consideration for tetanus immunization, damage control, debridement, wash, fasciotomy, pack, and stabilization. Although not all steps apply to every individual with a blast injury, they can serve as a reference to address the patient's key needs. 

Blast injuries often result in significant limb injuries. In the past, the approach to complex limb injuries was focused on a life over limb approach, often leading to amputation. Advances in vascular surgery have enabled more advanced limb-salvage techniques. There has been a shift from a survival-focused approach to one emphasizing functional preservation, patient autonomy, and reintegration. When possible, the patient should be involved in decision-making through shared consent. The final treatment decision must balance surgical feasibility with psychosocial and rehabilitative factors.

Results from various studies, including the Military Extremity Trauma Amputation/Limb Salvage and the Lower Extremity Assessment Project, highlight that elective amputation may yield comparable, if not superior, outcomes in some cases. These advances have been made possible due to advances in prosthetic technologies. However, successful outcomes rely not only on the surgical care but also on a long-term care team approach. The ultimate success is due to the successful integration of rehabilitation planning, shared decision-making, and patient empowerment throughout the continuum of care. 

A late complication of blast wave injury is traumatic aortic injury. Although rare, it is often fatal if not identified. Despite the absence of other significant primary blast injuries, an underlying aortic injury could persist. If there is a concern of a blast aortic injury, computed tomography imaging should be performed. Emergent thoracic endovascular aortic repair with stenting and thrombectomy is a potential life-saving procedure.[17][18][19][20][21][22](B3)

Differential Diagnosis

The differential diagnosis of blast injuries is broad and depends on the mechanism (primary, secondary, tertiary, quaternary, and quinary blast effects), the environment (confined vs open), and the organs involved. A structured approach by injury pattern is clinically useful.

Blast Injury Types

Primary blast injury (barotrauma from overpressure wave) primarily affects air-filled organs. The differential includes pulmonary contusion, pneumothorax (including tension), hemothorax, bronchopleural fistula, and acute respiratory distress syndrome. Tympanic membrane rupture must be distinguished from basilar skull fracture. Gastrointestinal perforation from barotrauma may mimic mesenteric ischemia, hollow viscus injury from blunt trauma, or spontaneous perforation. Blast-induced traumatic brain injury (mild to severe) must be differentiated from concussion due to blunt impact.

• Secondary blast injury (projectile/fragment injury) resembles penetrating trauma from gunshot or shrapnel wounds. The differential includes vascular injury (arterial transection, pseudoaneurysm), solid-organ laceration, hollow-organ perforation, and retained foreign bodies. These injuries may be occult and require CT angiography or operative exploration in unstable patients.
• Tertiary blast injury (body displacement) produces blunt trauma patterns similar to motor vehicle collisions or falls. Differential diagnoses include long-bone fractures, pelvic fractures, spinal fractures, intracranial hemorrhage (subdural, epidural, intraparenchymal), and solid organ injury.
• Quaternary injuries encompass burns, inhalation injury, crush syndrome, and toxic exposure. The differential includes carbon monoxide poisoning, cyanide toxicity (especially in enclosed explosions), compartment syndrome, and rhabdomyolysis with acute kidney injury.
• Quinary injuries (hyperinflammatory or toxic additive exposures) may present with unexplained hypotension, altered mental status, or systemic inflammatory response out of proportion to visible trauma; differential considerations include chemical exposure and sepsis.

While this list is not exhaustive, these are potential injuries that should be considered:

• Traumatic brain injury
• Globe trauma
• Skull fractures
• Facial fractures
• Perforated tympanic membrane
• Hemothorax, pneumothorax, or hemopneumothorax
• Rib fractures, including flail chest
• Hollow viscus injury (esophagus, stomach, small intestine, large intestine, gallbladder, bladder)
• Solid organ injury (liver, spleen, kidneys, pancreas)
• Genitourinary trauma
• Traumatic rhabdomyolysis and/or compartment syndrome
• Limb devascularization or amputation
• Chemical or thermal burns

In practice, clinicians must maintain high suspicion for occult hollow viscus injury, delayed bowel perforation, pulmonary barotrauma, and evolving intracranial pathology. In hemodynamically unstable individuals, early surgical exploration remains critical when imaging is inconclusive and clinical deterioration persists.

Prognosis

The prognosis of a patient with a blast injury depends on the extent of injuries and treatment. The effects of the blast injury can be permanent, such as amputation. The patient may need to learn to live with their residual injuries and adapt to a new way of life. This adjustment and final prognosis depend on the patient's engagement in their treatment and rehabilitation, as well as their support system.[23][24]

Complications

The complications of blast injuries vary with the type of device and the initial injuries to the patient. Each patient with a blast injury will have their own unique complications based on the injuries sustained. Traumatic brain injury may cause long-term cognitive deficits, while damage to the eyes and ears can cause long-term sensory deficits. Amputations may lead to phantom limb pain and contractures. This is not an exhaustive list of complications, but in addition to physical complications, every blast injury patient is susceptible to psychological distress and PTSD.[23][24]