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Blast injury

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Blast injury

Blast injury
Floor-by-floor breakdown of the injuries/deaths in the Alfred P. Murrah Federal Building from the April 1995 Oklahoma City bombing
Classification and external resources
eMedicine emerg/63
MeSH D001753

A blast injury is a complex type of physical trauma resulting from direct or indirect exposure to an explosion.[1] Blast injuries occur with the detonation of high-order explosives as well as the deflagration of low order explosives. These injuries are compounded when the explosion occurs in a confined space.

Contents

  • Classification 1
    • Primary injuries 1.1
    • Secondary injuries 1.2
    • Tertiary injuries 1.3
    • Quaternary injuries 1.4
  • Mechanism 2
  • Neurotrauma 3
  • Casualty estimates and triage 4
  • See also 5
  • References 6
  • External links 7

Classification

Diagram of a blast injury

Blast injuries are divided into four classes: primary, secondary, tertiary, and quaternary.

Primary injuries

Primary injuries are caused by blast gastrointestinal tract. Gastrointestinal injuries may present after a delay of hours or even days.[2] Injury from blast overpressure is a pressure and time dependent function. By increasing the pressure or its duration, the severity of injury will also increase.[2]

In general, primary blast injuries are characterized by the absence of external injuries; thus internal injuries are frequently unrecognized and their severity underestimated. According to the latest experimental results, the extent and types of primary blast-induced injuries depend not only on the peak of the overpressure, but also other parameters such as number of overpressure peaks, time-lag between overpressure peaks, characteristics of the shear fronts between overpressure peaks, frequency resonance, and electromagnetic pulse, among others. There is general agreement that traumatic brain injury has remained underestimated. Blast lung refers to severe pulmonary contusion, bleeding or swelling with damage to alveoli and blood vessels, or a combination of these.[3] It is the most common cause of death among people who initially survive an explosion.[4]

Secondary injuries

Secondary injuries are caused by fragmentation and other objects propelled by the explosion.[5] These injuries may affect any part of the body and sometimes result in penetrating trauma with visible bleeding.[6] At times the propelled object may become embedded in the body, obstructing the loss of blood to the outside. However, there may be extensive blood loss within the body cavities. Fragmentation wounds may be lethal and therefore many anti-personnel bombs are designed to generate fragments.

Most casualties are caused by secondary injuries as generally a larger geographic area is affected by this form of injury than the primary blast site as debris can easily be propelled for hundreds to thousands of meters.[5][6] Some explosives, such as nail bombs, are deliberately designed to increase the likelihood of secondary injuries.[5] In other instances, the target provides the raw material for the objects thrown into people, e.g., shattered glass from a blasted-out window or the glass facade of a building.[5]

Tertiary injuries

Displacement of air by the explosion creates a blast wind that can throw victims against solid objects.[2] Injuries resulting from this type of traumatic impact are referred to as tertiary blast injuries. Tertiary injuries may present as some combination of blunt and penetrating trauma, including bone fractures and coup contre-coup injuries. Children are at a particularly higher risk of tertiary injury due to their relatively smaller body weight.[5]

Quaternary injuries

Quaternary injuries, or other miscellaneous named injuries, are all other injuries not included in the first three classes. These include flash burns, crush injuries, and respiratory injuries.[5]

Traumatic amputations quickly result in death, and are thus rare in survivors, and are often accompanied by significant other injuries.[5] The rate of eye injury may depend on the type of blast.[5] Psychiatric injury, some of which may be caused by neurological damage incurred during the blast, is the most common quaternary injury, and post-traumatic stress disorder may affect people who are otherwise completely uninjured.[5]

Mechanism

Blast injuries can result from various types of incidents ranging from industrial accidents to terrorist attacks.[6] High-order explosives produce a supersonic overpressure shock wave, while low order explosives deflagrate and do not produce an overpressure wave. A blast wave generated by an explosion starts with a single pulse of increased air pressure, lasting a few milliseconds. The negative pressure (suction) of the blast wave follows immediately after the positive wave. The duration of the blast wave depends on the type of explosive material and the distance from the point of detonation. The blast wave progresses from the source of explosion as a sphere of compressed and rapidly expanding gases, which displaces an equal volume of air at a very high velocity. The velocity of the blast wave in air may be extremely high, depending on the type and amount of the explosive used. An individual in the path of an explosion will be subjected not only to excess barometric pressure, but to pressure from the high-velocity wind traveling directly behind the shock front of the blast wave. The magnitude of damage due to the blast wave is dependent on the peak of the initial positive pressure wave, the duration of the overpressure, the medium in which it explodes, the distance from the incident blast wave, and the degree of focusing due to a confined area or walls. For example, explosions near or within hard solid surfaces become amplified two to nine times due to shock wave reflection. As a result, individuals between the blast and a building generally suffer two to three times the degree of injury compared to those in open spaces.[7]

Neurotrauma

Blast injuries can cause hidden neurotrauma.

Individuals exposed to blast frequently manifest loss of memory of events before and after explosion, confusion, headache, impaired sense of reality, and reduced decision-making ability. Patients with brain injuries acquired in explosions often develop sudden, unexpected brain swelling and cerebral vasospasm despite continuous monitoring. However, the first symptoms of blast-induced neurotrauma (BINT) may occur months or even years after the initial event, and are therefore categorized as secondary brain injuries.[8] The broad variety of symptoms includes weight loss, hormone imbalance, chronic fatigue, headache, and problems in memory, speech and balance. These changes are often debilitating, interfering with daily activities. Because BINT in blast victims is underestimated, valuable time is often lost for preventive therapy and/or timely rehabilitation.[8]

Casualty estimates and triage

Explosions in confined spaces or which cause structural collapse usually produce more deaths and injuries. Confined spaces include mines, buildings and large vehicles. For a rough estimate of the total casualties from an event, double the number that present in the first hour. Less injured patients often arrive first, as they take themselves to the nearest hospital. The most severely injured arrive later, via emergency services ("upside-down" triage). If there is a structural collapse, there will be more serious injuries that arrive more slowly.[9]

See also

References

General
  • Editorial Board, Army Medical Department Center & School, ed. (2004). Emergency War Surgery (3rd ed.). Washington, DC:  
Specific
  1. ^ Blast Injury Translating Research Into Operational Medicine. James H. Stuhmiller, PhD. Edited by William R. Santee, PhD Karl E. Friedl, PhD, Colonel, US Army. Borden institute (2010)
  2. ^ a b c d Chapter 1: Weapons Effects and Parachute Injuries, pp. 1–15 in Emergency War Surgery (2004)
  3. ^ Sasser SM, Sattin RW, Hunt RC, Krohmer J (2006). "Blast lung injury". Prehosp Emerg Care 10 (2): 165–72.  
  4. ^ Born CT (2005). "Blast trauma: The fourth weapon of mass destruction". Scandinavian Journal of Surgery 94 (4): 279–85.  
  5. ^ a b c d e f g h i Keyes, Daniel C. (2005). "Medical response to terrorism: preparedness and clinical practice". Lippincott Williams & Wilkins. pp. 201–202.  
  6. ^ a b c Wolf, Stephen (July 23, 2009). "Blast injuries". The Lancet 374: 405–15.  
  7. ^  
  8. ^ a b Cernak, I., and L. J. Noble-Haeusslein. 2010. Traumatic brain injury: An overview of pathobiology with emphasis on military populations. J Cereb Blood Flow Metab 30(2):255-266.
  9. ^ "Explosions and Blast Injuries: A Primer for Clinicians" (PDF). CDC. Retrieved 2013-12-29. . Occasionally updated.

External links

  • Blast injury information from the CDC
  • Blast injury primer for clinicians
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