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Blast injuries result from the complex pressure wave generated by an explosion. Several factors affect the likelihood of blast injury:
- The first is the medium in which the explosion takes place; water is non-compressible so the pressure wave propagates rapidly with a slow rate of dissipation. It therefore has a greater potential for injury than an explosion in air.
- Second is the distance a person is from the explosion; the closer one is to an explosion, the greater the blast pressure experienced.
- Third is the site of blast. The blast pressure is amplified as pressure waves reflect back from solid surfaces and increase its force. So people in close proximity to a wall (eg in a confined space) will be subject to enhanced blast pressure and be at increased risk of injury.
Although terrorism is an ever-increasing concern, most blast injuries are caused by accidents such as gas explosions. The management will often involve implementation of the local major incident plan.
Blast injuries are divided into four categories:
- A primary blast injury is caused by the direct effect of blast overpressure on tissue. Air-filled organs (eg ear, lung, and gastrointestinal tract) and organs surrounded by fluid-filled cavities (eg brain and spinal cord) are particularly susceptible to primary blast injury.
- A secondary blast injury is caused by people being hit by debris that is physically displaced by the blast pressure wave. These can cause a combination of penetrating and blunt trauma injuries.
- A tertiary blast injury is caused by high-energy explosions and occurs when people fly through the air and strike other objects.
- Miscellaneous blast-related injuries include all other injuries caused by explosions, eg due to fire or collapse of buildings, burns, toxic substance exposures ( such as radiation, carbon monoxide poisoning, cyanide poisoning), asphyxia and psychological trauma.
Frequency depends on both the political stability of the region, eg terrorism, and local factors such as occupational health and safety priorities.
- Lungs may show evidence of pulmonary trauma and pneumothorax. The clinical picture of dyspnoea, cough and hypoxia is referred to as blast lung syndrome and represents impaired gas exchange and vascular shunting with ventilation mismatching. Pulmonary barotrauma can cause pleural tears or lacerations, which give rise to pneumothoraces, haemothoraces, pneumomediastinum, or subcutaneous air.
- Up to 94% of those with primary blast injuries will have a ruptured tympanic membrane. So some experts think that asymptomatic patients with intact tympanic membranes have a very low likelihood of occult pulmonary or intestinal primary blast injury. Conversely, rupture of tympanic membrane may, but not always, indicate additional, more serious injury.[4, 5]
- Abdominal injuries occur more commonly after underwater or closed-space explosions, owing to the heightened blast pressure and extended positive pressure phase. They may not be immediately obvious and serial examinations are often required. Intestinal haematoma or delayed perforation can take 12-36 hours to develop.
- Brain injuries are usually a consequence of secondary or tertiary blast injury and may include intracranial haemorrhage, direct parenchymal damage and cerebral contusion. After explosions, concussion and post-traumatic stress disorder are common and affected people experience substantial memory dysfunction and cognitive deficits.
- Musculoskeletal injuries are particularly common in combat situations where compartment syndromes and traumatic amputations may be a result of improvised explosive devices.
All investigations will be carried out by the emergency department but the following is a basic guide:
- Screening urinalysis to detect injury to the renal tract.
- If the explosion occurred in an enclosed space or was accompanied by fire, test carboxyhaemoglobin (carbon monoxide poisoning) and electrolytes to assess acid-base status.
- For major trauma, baseline haemoglobin, cross-match and screen for disseminated intravascular coagulation.
- If there is significant crush injury, compartment syndrome, or severe burns, rhabdomyolysis may cause hyperkalaemia and myoglobinuric renal failure.
- Burns from military white phosphorous munitions may cause hypocalcaemia and hyperphosphataemia. White phosphorus is a widely used component of military munitions, including hand grenades.
- CXRs are required for all those who have been exposed to high-pressure injury.
- If there is significant abdominal pain, abdominal X-ray (erect and supine) or abdominal CT scan (if haemodynamically stable) are used to detect pneumoperitoneum from bowel rupture.
- If there is any question of radiation or chemical contamination, decontamination of patients and equipment will be required.
- Blast lung injury induces poor lung compliance. When positive-pressure ventilation is needed, lung-protective techniques should be used, as positive-pressure ventilation can worsen pulmonary barotrauma and increase the patient's risk of arterial air embolism.
- There will inevitably be huge emotional as well as physical stress. Psychological help will be required from the outset and a calm, organised, supportive and caring approach to management of people involved in the accident is essential.
- Life support, including intravenous fluids and blood transfusions, may well be required at the site of the accident. However, fluid resuscitation needs to be carefully monitored, as therapies may be conflicting, eg haemodynamic instability dictates volume resuscitation, whereas excessive crystalloid can lead to pulmonary oedema in patients with pulmonary contusions.
- Specific treatments may also need to be considered.
- Cyanide poisoning:
- Consider cyanide poisoning in patients exposed to combustion in an enclosed space.
- Cyanide is produced by incomplete combustion of plastics.
- Treatment for cyanide poisoning should be started for significantly ill patients while awaiting confirmatory test results.
- Sodium thiosulfate and hydroxocobalamin are safe and appropriate empirical therapy.
Mortality rates vary widely.
- Mortality is increased when explosions occur in closed or confined spaces. 17-47% of people who die from explosions have evidence of pulmonary primary blast injury and 71% of those who are critically ill and hospitalised have pulmonary injury.
- Arterial air emboli arising from severe pulmonary injury can cause ischaemic complications, especially in the brain, heart and intestinal tract.
- Tympanic membrane rupture indicates that a high-pressure wave was present and may be associated with more severe organ injury.
Further reading and references
; British Orthopaedic Association (2014)
; (independent, non-profit organisation providing global education, information and communication resources for professionals in trauma and critical care)
; Blast injuries. Lancet. 2009 Aug 1374(9687):405-15. Epub 2009 Jul 22.
; Blast injury of the ear in a confined space explosion: auditory and vestibular Isr Med Assoc J. 2002 Jul4(7):559-62.
; Eardrum perforation in explosion survivors: is it a marker of pulmonary blast injury? Ann Emerg Med. 1999 Aug
; Otologic considerations of blast injury. Disaster Med Public Health Prep. 2010 Jun4(2):145-52.
; Spectrum of abdominal organ injury in a primary blast type. World J Emerg Surg. 2009 Dec 214:46.
; Pathology of blast-related brain injury. J Rehabil Res Dev. 200946(6):667-72.
; Blast injury research models. Philos Trans R Soc Lond B Biol Sci. 2011 Jan 27366(1562):144-59.
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