Blast Injuries Clinical Presentation

• If possible, determine what material caused the explosion.

  • High-order explosives (HEs) undergo detonation, an almost instantaneous transformation of the original explosive material into gases occupying the same volume of space under extremely high pressure. These high-pressure gases rapidly expand, compress the surrounding medium, and produce a defining supersonic, overpressurization blast wave. Examples of HEs include materials such as TNT, ammonium nitrate fuel oil, dynamite, and C-4 "plastic" explosives. In general, only HE explosions produce severe primary blast injury.
  • Low-order explosives (LEs) are composed of propellants, such as black powder, and pyrotechnics, such as fireworks. LEs undergo deflagration rather than detonation and release energy relatively slowly compared with HEs. This results in a subsonic explosion lacking the overpressurization blast wave that characterizes HEs. Although LE explosions can be deadly, LE explosions very uncommonly cause the pulmonary and central nervous system injuries unique to primary blast injury.
• If possible, determine the patient's location relative to the center of the explosion.

  • An explosion that occurs in an enclosed space (including a building, a mine, or a relatively lightly constructed enclosed space such as a bus) or in water tends to cause more serious injury.
  • Intensity of an explosion pressure wave declines with the cubed root of the distance from the explosion. A person 3 m (10 ft) from an explosion experiences 9 times more overpressure than a person 6 m (20 ft) away. Proximity of the person to the explosion is an important factor in a primary blast injury.
  • Blast waves are reflected by solid surfaces; thus, a person standing next to a wall may suffer increased primary blast injury.
• Because explosions often cause multiple casualties, anticipate activating the hospital or regional disaster plan.
• Another ominous consideration is the tactic of setting dual explosions. The initial explosion is intended to injure civilians and to attract law enforcement and rescue personnel, followed by a delayed explosion designed to injure rescuers. Hospital disaster plans should include tight security at all hospital entrances in the event of a terrorist explosion in the community. All hospital personnel should be alert for unattended packages.

  • In addition to protecting hospital patients and staff, sealing entrances helps control the chaotic flow of patients and visitors.
  • Industrial accidents and terrorist explosions may be associated with the release of toxic and/or radioactive materials. The Federal Bureau of Investigation (FBI) is particularly concerned about the possibility that a terrorist could attach a radioactive substance (eg, a radiopharmaceutical or part of an old radiography machine) to a conventional explosive device, causing radiation contamination of the scene and casualties. In the 1993 attack on the World Trade Center, terrorists attached cyanide to a bomb placed in the underground parking garage. Fortunately, in that incident the cyanide was destroyed by the combustion. Physicians and EMS personnel must diligently search for evidence of radiation and/or chemical contamination in persons with blast injuries.
  • Question plant managers, fire department officials, EMS personnel, and law enforcement personnel about these possibilities.
  • EMS agencies should check for radiation contamination at the scene of a deliberately caused explosion. In addition, hospital personnel should screen persons who have been exposed to deliberate explosions for radioactivity with a Geiger counter or similar radiation dosimeter. Each hospital has a radiation safety officer (usually a radiology technician) who can assist with this task.

• Examine lungs for evidence of pulmonary contusion and pneumothorax.

  • Assume that a patient's wheezing associated with a blast injury is from pulmonary contusion.
  • Other causes of wheezing in this setting may include inhalation of irritant gases or dusts, pulmonary edema from myocardial contusion, and adult respiratory distress syndrome (ARDS).
• Many experts recommend obtaining a chest radiograph in the presence of isolated tympanic membrane (TM) rupture since this may indicate exposure to significant overpressure. In a large series of victims of terrorist bombings, mostly involving closed spaces, 22% of patients with eardrum perforation had other significant injuries.

  • However, a patient with isolated TM perforation, but no other immediately identified injuries, does not automatically require an extended period of observation. In the above study, none of the 137 patients initially identified as having isolated TM rupture and well enough to be discharged developed later manifestation of pulmonary or intestinal blast injury.
  • Intact TMs do not imply the absence of serious injury, especially if the patient was wearing some type of hearing protection as is common in certain types of military or law enforcement operations.
• Abdominal injuries from explosions may be occult, and serial examinations are often required.

  • A recent large Israeli case series found that abdominal injuries occurred only as a result of massive trauma. This finding may be the result of selection bias, as all the explosions in their series occurred in open air. Air is a poor conductor of blast-wave energy, thus those who were subjected to enough energy to damage abdominal organs probably were situated near the explosive devices.
  • Other authors have reported occult injuries to both solid and hollow abdominal organs in people injured by closed-space explosions and blast injuries occurring in water.

Primary blast injury

Primary blast injury (PBI) is organ and tissue damage caused solely by the blast wave associated with HEs.

The leading edge of a blast wave is called the blast front. When a blast front reaches a victim, it causes an enormous, almost instantaneous rise in ambient pressure. For example, C4 explosions can create initial pressures of over 4 million pounds per square inch (30GPa).

Because explosive gases continue to expand from their point of origin, a longer negative underpressure (relative vacuum) follows the peak positive overpressure. Both the positive overpressure and the negative underpressure are capable of causing significant PBI.

Since air is easily compressible by pressure while water is not, gas-containing organs, especially the lungs, bowel, and middle ear, are most susceptible to PBI.

Pulmonary barotrauma is the most common fatal primary blast injury. This includes pulmonary contusion, systemic air embolism, and free radical–associated injuries such as thrombosis, lipoxygenation, and disseminated intravascular coagulation (DIC). ARDS may be a result of direct lung injury or of shock from other body injuries.

Thoracic PBI produces a unique cardiovascular response, observed nowhere else in medicine, that which is sufficient to cause death in the absence of any demonstrable physical injury. The immediate cardiovascular response to pulmonary blast injury is a decrease in heart rate, stroke volume, and cardiac index. The normal reflex increase in systemic vascular resistance does not occur, so blood pressure falls. This effect occurs within seconds. If this response is not fatal, recovery usually occurs within 15 minutes to 3 hours. However, even nonlethal PBI can impair pulmonary performance for hours to days.

Thoracic PBI may possibly result in pericardial tamponade even in the absence of penetrating trauma (secondary blast injury).^[6]

Acute gas embolism (AGE), a form of pulmonary barotrauma, requires special attention. Air emboli most commonly occlude blood vessels in the brain or spinal cord. Resulting neurologic symptoms must be differentiated from the direct effect of trauma.

Intestinal barotrauma is more common with underwater than air blast injuries. Although the colon usually is affected most, any portion of the GI tract may be injured.

The ear is the organ most susceptible to primary blast injury. Acoustic barotrauma commonly consists of TM rupture. Hemotympanum without perforation also has been reported. Ossicle fracture or dislocation may occur with very high-energy explosions.

PBI of the brain may be associated with impaired cerebral vascular function including compensatory mechanisms for traumatic brain injury. Reactive oxygen species, including superoxide anion radical and nitric oxide, are likely major contributors.^[7]

Secondary blast injury

Secondary blast injuries (SBIs) are caused by flying objects striking individuals.

This mechanism is responsible for the majority of casualties in many explosions. Penetrating thoracic trauma, including lacerations of the heart and great vessels, is a common cause of death in the setting of SBIs. For example, the glass facade of the Alfred P. Murrah Federal Building in Oklahoma City shattered into thousands of heavy glass chunks that were propelled through occupied areas of the building with devastating results.^{[8, 9]} During the 1998 terrorist bombing of the US Embassy in Nairobi, flying glass wounded people up to 2 km away.

Military explosive casings (eg, hand grenades) are specifically designed to fragment and to maximize damage from flying debris (shrapnel).

Civilian terrorist bombers (eg, Olympic Park in Atlanta) often deliberately place screws or other small metal objects around their weapons to increase secondary blast injuries.

Tertiary blast injury

Tertiary blast injuries are caused by individuals flying through the air and striking other objects, generally from high-energy explosions.

Unless the explosion is of extremely high energy or focused in some way (eg, through a door or hatch), a person with tertiary blast injury usually is very close to the explosion source.

Together with SBIs, this category accounted for most of the pediatric casualties in the Oklahoma City bombing. A high incidence of skull fractures (including 17 children with open brain injuries) and long-bone injuries including traumatic amputations occurred.^[10]

Quaternary blast injury

Miscellaneous blast-related injuries, sometimes termed quaternary blast injury, include burns (chemical or thermal); injury from falling objects; crush injuries from collapsed structures and displaced heavy objects; falls resulting from the explosion; and toxic dust, gas, or radiation exposure. Acute methemoglobinemia has been reported after nitroglycerine transcutaneous absorption resulting from a bomb explosion.^[11]