The wounding patterns of blast injuries are well known to any military medic who has served recently on operations, with Improvised Explosive Devices (IEDs) constituting a significant proportion of the casualties on the battlefields of Iraq and Afghanistan. Sadly the IED threat is no longer confined to war zones, with a series of high profile, mass-casualty IED terror events occurring in places of mass gathering in first-world countries in recent years.

Terrorists have come to favour explosives because of their proven ability to inflict mass casualties, cause fear and disruption in the community, and attract media interest (ANZCTC 2016).

Recent mass-casualty events of international significance include the Boston Marathon bombing of April 2013, the Charlie Hebdo shootings of January 2015 and the November attacks in Paris the same year. More recently we have seen the airport bombings in Brussels and Istanbul, and once again another mass-casualty terrorist attack in Nice, France when a truck drove into crowds on 14 July 2016, killing 84 people and injuring in excess of 300 more.

Turkish President Recep Tayyip Erdogan made the following poignant statement on the day of the Istanbul Airport bombing:

 “The bombs that exploded in Istanbul today could have gone off at any airport in any city around the world” (bbc.com, 2016)

With that thought in mind, it is important that first responders and civilian medical staff have an understanding of the patterns of injury associated with blasts, as to be best prepared for the very real possibility that a mass-casualty incident occurs in their city. There are some outstanding lessons to be learned from the experiences of the French medical responders in the wake of the multisite terror attacks around Paris in November 2015 (Hirsch M 2015), and I encourage readers to pursue that reference. This article presents an overview of the specific wounding patterns of blasts to better inform medical responders of the constellations of injury patterns following blasts, as to be able to manage not only the obvious, but also the unseen life-threatening injuries.

Injuries from IED blasts occur from a variety of different mechanisms relating to the specific causative mechanism. It is internationally accepted that there are four distinct phases of blast injury (CDC 2016), which are presented below. Naturally these specific injury patterns don’t occur in isolation, and will occur concurrently in the blast-injured patient. It is however useful to study them in isolation, and it is important for the treating medical team to be aware of the less obvious internal injury profiles associated with blast injuries. For the first responder, the highest priority is always stopping catastrophic bleeding.

Primary Blast Injury

Primary blast injury results from the over-pressurisation wave emanating from high-explosive charges interacting with body surfaces. It primarily affects the gas filled-structures of the body including the lungs, intestines and eardrums, in extreme cases causing these structures to rupture. It can also result in eyeball rupture and Traumatic Brain Injury and concussion.

The invisible blast pressure wave travels just in front of the explosion and debris caused by the blast and is illustrated nicely in the following slow motion video of a high-explosive blast.

Primary blast injury occurs due to changes in velocity of the blast pressure wave as it moves between tissues of different densities. When this occurs, the blast wave either accelerates (when moving from high to low densities) or decelerates (when moving from low to high densities). These changes in velocity of the blast wave cause increased energy to be dissipated into the surrounding tissues resulting in damage. The best example is perhaps as the blast wave passes through the chest of a casualty. Initially the wave hits the chest wall and decelerates as it begins to move through the skin, soft tissues, muscles and bones of the chest wall. As the blast wave moves into the air-filled lungs however the density of the tissue decreases significantly and the blast wave accelerates, causing increased damage. The opposite occurs as the wave hits the other side of the chest wall and decelerates again, once again causing increased damage. The resultant injury to the lung is known as blast lung, and can cause insidious deterioration in lung function over a period of hours to days after blast exposure as fluid leaks into the lungs as a result of the damage caused by the pressure wave.

The images below show a diagrammatic representation of a blast wave passing through a cross-sectional CT scan of a chest, as well as an actual (paediatric) blast lung casualty on X-ray and CT scan (Barnard & Johnson 2013). The fluffy-looking opacities radiating out from the centre of the X-ray and CT scan are caused by the blast-damaged lung leaking fluid into the air spaces.

The most memorable blast lung casualty that I’ve been involved with was sadly a 9-month-old girl in Afghanistan. She had been travelling in a vehicle with her family of eight when it had struck a massive IED intended for one of our armoured military vehicles. The blast tore the vehicle in half killing four of the occupants instantly, with a fifth dying shortly after.

Of the surviving three, one, the child’s mother, had severe spinal injuries and was rendered densely paraplegic from the mid-chest down. The other survivor, the little girl’s toddler brother had open injuries to his abdomen, had lost toes and fingers and had an open skull fracture with his brain on show (pictured below in Tertiary Blast Injury). Despite the devastation of the blast, the little girl had seemingly no more injuries than a superficial graze to her forehead. It was suspected that the mother had been cradling her at the time of the event and had shielded her from the blast. Whilst it initially appeared as a miracle, the little girl began to develop significant breathing difficulties within 24 hours of injury and despite intubation and ventilation to try and manage her lung injury; she deteriorated and died by the 48-hour mark.

It can be appreciated that the same blast pressure wave can destroy the wafer thin eardrum, and disrupt the tiny bones behind it that transmit the vibrations that are interpreted by our brains as sound.

There is also a growing body of literature surrounding the longer-term sequelae of blast waves to the brain itself, with hundreds of thousands of returned troops being diagnosed with Mild Traumatic Brain Injury (MTBI) as a result of a blast exposure (medicalxpress 2015). Even with no external physical damage to the casualty, the pressure wave of a nearby blast can cause long-term scarring on the brain as seen in the image below. Owing to its delayed presentation, this MTBI from blast is categorised by most as a quaternary blast injury.

Obviously the degree of primary blast injury sustained is dependent on many variables, the main factors being the size of the explosion, the distance from the explosion that the casualty was, and any form of shields between the casualty and the blast. In the pre-hospital setting the first responder should always check for ruptured eardrums in any blast casualty (at the appropriate stage in their secondary survey). If present, a ruptured eardrum should alert the first responder that a significant primary blast injury has occurred and that the casualty may have sustained a significant lung or intestinal injury as well, and needs urgent evacuation to an appropriate facility for further investigation and management.

Secondary Blast Injury

Secondary blast injury results from flying high-velocity debris and bomb fragments penetrating the casualty’s body, and may affect any body part. The extent of damage done by secondary blast injuries is influenced by a multitude of factors including the location of the explosive device relative to the casualty, the materials used to construct the device, and as with primary blast injuries, the distance of the casualty from the blast.

A good illustration of secondary blast injury is the example of a dismounted soldier standing on a pressure-plate IED, such as that commonly found in both Iraq and Afghanistan. In this instance the blast originates from under the soldier and explodes upwards. Often IEDs would be encased in a metal structure, such as a large artillery shell, and be filled with rocks, nails, bolts and other metal debris. With the initiation of the device, every single piece of shrapnel in the device is propelled upward and takes on its own ballistic properties based on the charge propelling it and the mass and shape of the shrapnel. The use of a metal case focuses the blast in a set direction. When it strikes the casualty, each individual piece of shrapnel has a ballistic profile of its own and in unison act like a huge shotgun shell to deliver the devastating injuries seen from dismounted IED strikes.

The following image is of the individual pieces of shot from a 12-gauge shotgun shell fired into ballistic gelatin. The shrapnel from an IED acts in a similar fashion with each individual piece forming its own wound based on its shape, size, weight and the charge behind it. In the image below, a dark area can be seen where the shot has completely destroyed the gelatin and left a cavity. The same occurs with IED blasts, accounting for the massive amounts of tissue damage caused by them.

In the setting of the traumatic amputations from IED blasts seen in the images above, the casualty has minutes to live if their arterial bleeds are not controlled. The lifesaving intervention seen in both the lower limb photos is the timely application of arterial tourniquets by others on scene at the point of injury. A detailed description of the history of arterial tourniquets, historical and contemporary literature on their use, appropriate application, as well as lessons learned from years of TQ use on special operations by the TacMed community can be found in TacMed’s new Ebook. The Ebook is titled “Arterial Tourniquets for Police Officers, Law Enforcement and Other First-Responders” more information on the publication can be found here.

IED tactics, techniques and procedures used by terrorists in war zones are now concerningly finding their way onto the streets of our cities. In the aftermath of the Boston Marathon bombing it was ascertained that the IED used was a metal pressure cooker filled with nails and ball bearings (nydailynews.com) similar to the one illustrated below.

The device was placed at street level and resulted in injury profiles very similar to those seen in war zones, including 17 traumatic lower limb amputations (King et al. 2015)

Tertiary Blast Injury

Tertiary blast injury results from casualties being thrown by, or having limbs flail in the blast wind, and may affect any body part. Tertiary blast injuries can include fractures, traumatic amputations, and closed and open brain injuries. When casualties are thrown by the blast wind and strike a wall or other object, the injury profile caused is typically blunt trauma and often results in fractures. Another form of tertiary blast injury is seen in vehicle IED strikes, where instead of the casualty being thrown, the floor of the vehicle is in effect thrown into the feet of the casualties. The result is once again blunt trauma injuries, often involving severe lower limb fractures of restrained passengers, and potential spinal injuries of unrestrained and standing passengers (such as in turrets of armoured vehicles) as they are either propelled into the roof of the vehicle, or ejected from it completely.

The traumatic amputations resulting from tertiary blast injury differ from those caused by secondary blast injury in that, instead of the tissue being shredded away by the shotgun effect of the shrapnel, the limbs are actually torn off by the blast wave. This often results in the disarticulation of the limb through a joint, such as pictured below. Naturally this is purely academic for the first-responder, and the immediate management remains the same, that being placement of a timely arterial tourniquet.

As casualties are thrown by the blast wave, tertiary blast injury also constitutes both closed and open head injuries due to blunt force trauma. The image below is a young casualty from the demolished car seen in earlier images above. Whilst he miraculously survived the massive blast, he sustained a significant open skull fracture.

Quaternary Blast Injuries

Quaternary blast injuries include all other explosion-related injuries, illnesses, or diseases not due to primary, secondary, or tertiary mechanisms. Quaternary blast injuries include burns, crush injuries, lung injuries from smoke inhalation and delayed presentations of Traumatic Brain Injury (as discussed above). Burns are a significant concern in casualties in close proximity to an IED blast, as can be appreciated from the photo below of one of the two Boston Marathon IEDs initiating.

Whilst any body part can be affected by burns from an IED blast, a high index of suspicion needs to be held for inhalation burns in casualties who have been in close proximity to a blast. Any casualty with obvious facial burns, singed facial hair or eyebrows, or carbonaceous material in their mouth on assessment may be at risk of imminent airway loss due to swelling from airway burns. Harsh, grating sounds heard on breathing are a strong indicator of impending airway loss and a definitive airway is likely to be required. Because the airway is swelling shut at the level of the vocal cords, nasopharyngeal, oropharyngeal and supraglottic airways such as Laryngeal Mask Airways (LMA) are ineffective in managing inhalation burns. Intubation or surgical airway is required to secure the airway (the latter of which can be seen in the neck of the casualty in the second photo below).

Whilst the list of potential quaternary blast injuries is long, one final injury worth considering is that of blood-borne viruses. This is of particular concern with suicide bombers who may be wearing the device as a vest, causing their bones and body parts to become projectiles on detonation. Even in the absence of a suicide vest, shrapnel from an IED can easily pass through one casualty and lodge in another, creating yet another long-term medical liability of tracking casualties and testing them for blood-borne viruses. The process for tracking and testing casualties from the Boston Marathon bombings is described by Brunner et al. (2014) in their paper titled “Terrorist Bombings: Foreign Bodies from the Boston Marathon Bombing.”

Naturally, when presented with an IED blast casualty, all of the injuries described above may be present to varying degrees and will compound each other. Key factors which will determine casualty survivability following an IED blast include the size and nature of the device, as well as the proximity of the casualty from the blast and any shields between them and the blast. Casualties close to a large blast are unlikely to survive due to the cumulative effect of all the different forms of blast injuries summing to injuries immediately incompatible with life.

With smaller devices, casualties are likely to survive if massive haemorrhage from injuries such as limb amputations is controlled in a timely fashion by first-responders. This was the case at the Boston Marathon bombings, with haemorrhage control measures being initiated rapidly following the blasts, coupled with short transit times to tertiary hospitals. Application of military haemorrhage control measures including arterial tourniquets and haemostatic dressings need to be adopted by civilian emergency response services to optimize their response to such an incident. Survival rates following a large blast increase as distance from the device increases. Those close to the blast are likely to be killed instantly, or die from wounds shortly after, however as distance from the device increases, the effects of all four above-described blast wound profiles decreases. The emotive image below illustrates this point nicely with fatalities seen close to the blast, sitting casualties further out and walking wounded in the distance.

With their relative ease of production and their proven ability to inflict massive amounts of harm when properly deployed, it is easy to see why Improvised Explosive Devices have become the preferred weapon of terrorists worldwide. From the perspective of a medical responder to a mass-casualty IED event, it is important to understand the various profiles of blast injury in order to optimally respond. The obvious external injuries should be treated as per any other mechanism of injury, however it is the unseen injuries that must be looked for in blast casualties. These include the potential for inhalation burns, consideration of blast lung and other hollow organ damage from the blast wave, as well as closed head injuries and the longer-term potential for MTBI. Finally consideration needs to be given to blood-borne virus transmission in an IED attack.

Unfortunately this article no longer pertains only to military medical personnel deploying to war zones. The terrorists of the world are bringing these weapons to the streets of our cities, and it is time for civilian medical responders to adopt the military-inspired equipment and techniques to manage them.

As always questions and comments are welcome, and once again anyone interested in the TacMed Arterial Tourniquet Ebook can find it now at Amazon.com.

Kind regards, dan.

Featured image courtesy of esquire.com

References

Australia-New Zealand Counter-Terrorism Committee 2016, Improvised Explosive Device (IED) guidelines for places of mass gathering, Attorney-General’s Department, Barton, ACT.

Barnard, E, Johnston, A 2013, ‘Images in clinical medicine. Blast lung’, New England Journal of Medicine, vol. 14, no. 383(11), p. 1045.

BBC 2016, ‘Istanbul Ataturk airport attack: 41 dead and more than 230 hurt’, BBC News, viewed 25 September 2016,<bbc.com>.

Brunner, J, Singh, AK, Rocha, T, Havens, J, Goralnick, E, Sodickson, A 2015, ‘Terrorist bombings: foreign bodies from the Boston Marathon bombing‘, Seminars in Ultrasound, CT and MRI, vol. 36, no. 1, pp. 68-72.

Centre for Disease Control 2016, Explosions and Blast Injuries: A primer for clinicians, CDC Injury Prevention, Department of Health and Human Services USA. Viewed 25 September 2016 <http://www.cdc.gov/masstrauma/preparedness/primer.pdf>

Hirsch M, C, Nizard R, et al. 2015, ‘The medical response to multisite terrorist attacks in Paris’, The Lancet,<http://www.thelancet.com/pb/assets/raw/Lancet/pdfs/S0140673615010636.pdf%3E.>.

King DR, L, Ramly EP, BostonTraumaCollaborative 2015, ‘Tourniquet use at the Boston Marathon bombing: Lost in translation’, The Journal of Trauma and Acute Care Surgery, vol. 78, no. 3, pp. 594-599.

Medicalxpress 2015, ‘MRI shows ‘brain scars’ in military personnel with blast-related concussion’, viewed 20 September 2016,<http://medicalxpress.com/news/2015-12-mri-brain-scars-military-personnel.html>.