The war being fought in Iraq (2003–2009) and Afghanistan (2006–present) is unconventional in that British forces are predominantly engaged in counterinsurgency tactics as part of an asymmetric war[1]. While US and coalition forces have numerous technological advantages over the enemy in terms of weapons, armour, transportation and a high level of organisation, they face unconventional weapons and tactics in accordance with a less organised opposition. As a result, the patterns of injury most often encountered in wounded soldiers reflect the enemy’s dependence on improvised explosive devices (IEDs), mines and rocket-propelled grenades (RPGs)[2].

Introduction
 The types of war wounds produced by high energy weapons present very different medical and surgical challenges to those previously encountered on the battlefield and to those seen in the civilian setting. Explosion-related injuries create challenges on numerous levels, which will be discussed in this paper based on experience of these wounds at the UK role 4 facility, The Royal Centre for Defence Medicine (RCDM), Queen Elizabeth Hospital, Birmingham University NHS Trust.


Modern war wounds
Gunshot wounds are still frequently seen on injured soldiers, however, explosion-related injuries are now the most common type of injury[3]. The catastrophic trauma that occurs as a result of explosive devices is devastating in contrast to other forms of battle injury. It would therefore be expected that the mortality rate associated with such injuries is much higher today than in previous wars. However, this has not been the case. The mortality associated with war wounds has significantly declined due to a number of factors[4]:

• Improvements in body armour have resulted in lower rates of thoracic injury
• Field medical units provide a high quality of immediate care resulting in better pre-hospital chances of survival
• Transportation from the war zone to role 4 facilities may often be achieved within 24 hours of the incident[5].

It is therefore understandable that increased injury-severity scores are being seen in soldiers who survive such catastrophic injuries[6].

The destructive extent of an explosion is dependent on the nature of the device and the proximity of the soldier when it detonates[7]. In contrast to other forms of weapon (ie firearms), explosive devices have the capacity to injure multiple victims simultaneously by a variety of different mechanisms. Detonation of an explosive device results in the instantaneous conversion of explosive material to a high pressure gas. The supersonic expansion of this gas creates a blast wave through space that compresses air at its leading edge forming a high-pressure shock wave, the 'overpressure'[8]. The negative pressure void created in the wake of the overpressure sucks debris into the air, which is then caught and propelled outwards by the 'blast wind' - the mass outward movement of air that follows the overpressure. There are five classes of injury associated with explosive devices, however as victims of blast injuries have multiple wounds involving different bodily systems, injury patterns tend to become less distinct[7,9].
Primary blast injury results from the overpressure as it passes through the body; specifically at air-fluid interfaces, ie the tympanic membrane, lungs and bowel[3], where the rapid compression/expansion and acceleration/deceleration forces cause significant tissue damage. The extent of primary injury is dependent on the distance of the victim to the explosion epicentre, the size and type of device, and the environment in which the explosion occurs[7]. The damaging extent of blast waves in an enclosed space is much greater due to the multiplying effect of deflected waves off walls and objects[9].

Secondary explosive injuries are due to high-energy penetrating fragments from the device casing, or often in the case of improvised explosive devices (IEDs), from fragments such as rusty nails and scrap metal placed within the device to increase its destructive capacity[10]. While these penetrating wounds are ballistic in nature, they differ significantly to those caused by bullets. The irregular shape of fragments causes them to lose speed through the air so that their trajectory through the tissues is slower and much more tortuous than that of a streamlined bullet.
While these factors may initially result in a less severe injury than that of a high-velocity bullet, blast fragments are more numerous and carry much more debris into the wounds leading to extensive wound contamination[11]. It is this secondary mechanism of blast injury that causes catastrophic trauma to extremities and results in bone and soft-tissue damage.

Tertiary explosive injuries describe blunt trauma resulting from translocation of the victim into the ground and other structures, or injury secondary to being hit by flying objects. Crush and penetrating trauma may result from this mechanism of injury.

Quaternary explosive injuries involve other mechanisms associated with explosions such as burns, inhalation of toxic gases and injury from environmental contaminants. The category described as quinary injuries is a relatively recent addition and allows for the purposeful addition of radioactive or bacterial substances to IEDs, creating a 'dirty bomb'. These are increasingly being seen in acts of terrorism[12].
Injuries resulting from explosive devices are consequently both multiple and complex. In the majority of cases, victims of explosive injuries on the battlefield present with heavily contaminated extremity trauma involving massive destruction of soft-tissue and bone. Less obvious effects of this type of injury include microvascular damage in the area surrounding trauma,  which later affects reconstruction and healing. The management of such injuries requires a holistic approach by a multidisciplinary team and is complicated by the need to rapidly transport the injured soldier from the battlefield back to the UK.

Phases of management
From the moment that a soldier is injured medical management protocols are set in motion, the efficacy of which greatly determines the casualty's outcome and further management prospects. Military medical support is organised in four tiers: roles 1 to 4[13]. Each level is supported and resupplied by the role above it, with role 4 being the RCDM in the UK.

Ahead of deployment, all military personnel are issued with field dressings, morphine and a one-handed application combat tourniquet, before being trained in their use[14]. By administering immediate self or buddy first-aid treatment in the field, blood loss may be minimised and the chance of survival is improved before treatment by a trained role 1 medic. There are roughly five trained medics to each platoon of approximately 30 soldiers.
These medics constitute the role 1 facility and play a similar role to that of paramedics in the civilian world - providing battlefield life support (management of catastrophic bleeding, airway, breathing and circulation)[15].
Medical provision at forward operating bases (FOBs) is a role 2 facility, which provides both everyday and emergency care to patrols operating from the FOB. It also serves as a point of primary retrieval via helicopter by a medical emergency response team (MERT) to the role 3 facility field hospital at Camp Bastion. Here, consultant lead emergency, intensive care and surgical facilities employ methods of damage control, resuscitation and surgery.
The aim is to restore physiological function (as opposed to anatomical function)[16] and limit the lethal triad of coagulopathy, hypothermia and metabolic acidosis encountered as a result of prolonged operative time and persistent bleeding in multiply injured soldiers[14,17].
One of the key principles in optimising the survival of acutely injured soldiers is damage control resuscitation (DCR), which begins at role 2 facilities and is continued at the role 3 field hospital. Damage control surgery, an aspect of DCR, occurs at the role 3 facility in three distinct phases in order to maximise chances of survival:

• Primary operation and haemorrhage control
• Critical care
• Planned reoperation[18].

The principle of damage control surgery relies on further definitive management at the next level of care in the UK.