The numerous casualties of war facilitate the collection and evaluation of data on trauma management. Massive haemorrhage is the underlying cause of mortality in a significant proportion of military personnel killed or fatally injured on the battlefield. Retrospective analysis of the management of these casualties combined with experimental research in animal models resulted in the advocacy of Damage Control Resuscitation (DCR), which includes the use of hypotensive resuscitation, the prevention and treatment of elements of the lethal triad of hypothermia, acidosis and coagulopathy, and an innovative approach to infusion of blood products. Guidelines have been drawn up for the identification of those on whom DCR confers the best chance of survival. Technological advances have facilitated data analysis and audit of case management in these casualties, leading to evidence-based alteration in clinical practice and improved patient outcome.

Introduction

Throughout history, wars have taught us invaluable medical lessons particularly in the area of trauma. The American Civil War brought about the development of field hospitals due to the discovery of the link between immediate treatment and survival rates. In World War I psychological trauma was recognised for the first time as a serious illness and blood banks were pioneered, with blood transfusions becoming common practice. World War II saw innovation in the surgical field, particularly in orthopaedics, due to the number of emergency procedures which were required to take place. During the Korean War, mo- bile hospitals were developed so that an injured soldier was never too far from medical attention, while the Vietnamese war saw helicopters emerge as a way to transport critical patients [1]. In more recent years, the wars in Iraq and Afghanistan have led to some of the most important discoveries in trauma medicine of the 21st century, particularly in the region of resuscitation. Such experiences from the military are important as they are often subsequently incorporated into civilian practice. 

why are these advances made during times of war?

It is presently thought that approximately 7% of combat casualties are in need of massive transfusion [2]. This has influenced the practice of resuscitation enormously. In civilian medicine, life-threatening trauma constitutes a very small proportion of patients attending a large number of geographically distinct emergency departments [3] leading to difficulty in accumulating and analysing data. The reason such rapid advancements are made in times of war is due to the large number of casualties and the collection and evaluation of data. The use of this data has been optimised in the 21st century due to innovations in technology which allow for accurate and rapid analysis.

American casualties in Afghanistan pass down a specifically structured chain of management, further facilitating data audit. The first response to a casualty is from the combat medic who travels as a part of each team on manoeuvres. A helicopter retrieves the wounded from their position within an hour and takes them to the closest resuscitation unit from where they are transferred to a military base hospital in Germany within two hours. If more sophisticated care is required the patient is flown to one of two major US military hospitals. This definitive chain allows for excellent standardisation of data collection. The data is analysed and improvements are made, providing a continuous loop of quality analysis and quality improvement in medical care. 

DAMAGE CONTROL RESUSCITATION

Uncontrolled haemorrhage has been identified as the cause of death in approximately 40% of trauma related cases (4). Clearly, the management of trauma was unsatisfactory and so research was devised to identify how management of patients with exsanguinating haemorrhage could be made more effective. The result was Damage Control Resuscitation (DCR), which is the protocol now used to treat all severely injured battlefield casualties. It evolved during the Afghanistan war due to the large number of patients requiring massive transfusions in an attempt to manage both the risk of haemorrhage and coagulopathy [5]. DCR includes the use of hypotensive resuscitation; the prevention and treatment of hypothermia and acidosis and an innovative approach to blood transfusion. DCR can be divided into two phases, hypotensive resuscitation and haemostatic resuscitation. 

Hypotensive Resuscitation

The body’s natural defences against exsanguination are considerable and should be recognised in treatment. For example, if an artery is completely transected, the resulting hypotension due to initial blood loss along with vasoconstriction and coagulation can be extremely efficient in stopping haemorrhage. Traditionally in cases of haemorrhagic shock, intravenous (IV) fluids were given until a blood pressure of 120mmHg systolic pressure was achieved. However, this works against the body’s natural defence mechanism which allows blood pressure to remain low in order to minimise blood loss. Therefore, in the Iraq and Afghanistan wars it has become standard to aim for a systolic blood pressure of approximately 90mmHg and a conscious, responsive patient. This is thought to maximise the resuscitation benefit to the mitochondria while minimising the chances of “popping a clot” and causing even further bleeding [5]. Though this approach is supported by a significant number of studies and has proven to be effective, it is important to remember that the evidence from these wars is based on young, fit and healthy soldiers and is therefore not an accurate representation of the population at large. For example if a sixty year old man with coronary artery disease presented with haemorrhagic shock it would be inadvisable to follow this course of action as a myocardial infarction could result from maintaining this patient’s blood pressure at 90mmHg systolic. In much the same way, a patient with carotid artery disease could suffer from a stroke in these circumstances. It is very important, therefore, to implement sound clinical judgement when using this form of resuscitation. 

The Lethal Triad and Haemostatic Resuscitation

The ‘lethal triad’ refers to a combination of hypothermia, acidosis and coagulopathy and is seen in patients who have suffered severe trauma. It is associated with a considerable increase in mortality rates [6]. It is further complicated by the fact that each component of the triad can exacerbate the other two. The second phase of DCR – haemostatic resuscitation – is concerned with the lethal triad and attempts to minimise acidosis and hypothermia. DCR recognises the fact that coagulopathy is the most easily treatable element of the triad and therefore aims to immediately correct it.

Acidosis

Hypovolaemia and peripheral vasoconstriction cause inadequate perfusion of peripheral tissues, causing anaerobic cellular respiration which leads to an accumulation of lactic acid and consequent metabolic acidosis. How acidosis negatively affects the coagulation cascade is not fully understood, how- ever studies have shown acidosis to have harmful effects on the prothrombinase complex, platelets, thrombin generation and fibrinogen concentration [7][8]. It can be difficult to reverse acidosis in a patient who is still haemorrhaging as its reversal is dependent on reperfusion of peripheral tissues. Currently, studies are being carried out to ascertain whether the administration of exogenous bicarbonate or tris-hydroxymethyl aminomethane can combat the negative effects of acidosis on the coagulation system [9] [10].

Considering the difficulties in reversing acidosis, it is extremely important to avoid any actions which can worsen this condition. An important example is that of hypoventilation which is easily managed by adequately ventilating the patient. Also of importance when considering acidosis, is the choice of resuscitation fluid. Normal saline, which is one of the most commonly used isotonic crystalloid fluids, has a pH as low as 4.5 and has been proven to contribute to metabolic acidosis in patients suffering from shock [11]. 

Hypothermia

Hypothermia refers to the drop in core temperature to below 35 degrees Celsius at which point bodily functions and metabolism cannot be carried out as normal. The effect hypothermia has on survival rates is clearly described and severe trauma-related hypothermia (<32 degrees Celsius) has been associated with 100% mortality [12]. The coagulation cascade is an enzymatic pathway and is therefore sensitive to changes in temperature. Hypothermia affects coagulation in two ways; moderate hypothermia (32-34 degrees Celsius) directly reduces coagulation factor activity by approximately 10% for each temperature decrease of one degree, while significantly reducing the activity of platelets [13][14][15][16]. Hypothermia also shifts the oxygendissociation curve, making oxygen less readily available to tissues for cellular respiration [14]. This leads to anaerobic respiration and consequent acidosis.

Trauma patients at war are susceptible to hypothermia for a number of reasons. In general, wounding occurs outdoors, severe injury renders the casualty immobile, and loss of blood slows down metabolic activity. All of which contribute to a drop in core body temperature. Due to the association of hypothermia with a decreased survival rate, a new protocol was established by the US military in Iraq with an emphasis placed on pre-hospital management of the patient regarding hypothermia prevention. Combat medics were trained in basic principles on how to avoid hypothermia such as the rapid control of external haemorrhage, limited removal of patients’ clothing, and the use of thermal blankets and in-line fluid warmers, for example, the Thermal Angel. These in-line fluid warmers keep blood and fluids warm – between 37 and 42 degrees celcius – by delivering warm fluids at rates of up to 5000ml per hour. The Thermal Angel is particularly useful in trauma situations as it is disposable, lightweight and completely portable. Easy to set up, it provides warm fluids within 45 seconds. This protocol has been highly effective and the number of casualties arriving to military hospitals with hypothermia is now decreased from 7% to 1% [17].

Coagulopathy and Blood Transfusions

Coagulopathy is a defect in the body’s ability to form clots leading to bleeding diathesis. It was thought up until recently that coagulopathy occurred primarily due to the dilution of clotting factors after the infusion of crystalloids. However, new research has concluded that a large percentage (38% in one study), of casualties were already coagulopathic on admission to hospital before the administration of any fluids [18]. Traditional methods of resuscitation involve administering IV crystalloid and blood at a ratio of 3:1. Fresh frozen plasma and platelets – which provide the clotting factors – were only given after 8-10 units of blood, due to the fact that many patients were not identified as coagulopathic at this stage of treatment.

There is a significant scientific basis for the early administration of coagulation factors for patients requiring massive transfusion [19][20][21][22] and recently studies have recommended a 1:1:1 ratio of packed red blood cells, fresh frozen plasma and platelets - this is the protocol now followed by the US and UK militaries which is slowly being translated to civilian practice. There are a variety of positive effects associated with this new transfusion protocol. Firstly, superior clotting ability is observed as the clotting factors are administered earlier, decreasing the possibility of coagulopathy and consequently the amount of blood lost. The ‘Michelin Man Effect’ refers to peripheral oedema and is a result of crystalloid infusion. As crystalloids are not transfused as part of this protocol there is a decrease in the ‘Michelin Man Effect’. Orthopaedic surgeons in the American military hospitals have commented on how much easier their surgeries are due to this decrease in oedema and have noted that they see less post-operative complications in patients with- out the ‘Michelin Man Effect’.

The benefits of freshly donated blood have also become apparent in recent years. Donated blood has a shelf life – approximately 5 weeks for white blood cells and 6 weeks for red blood cells – but the older the blood is, the less clotting factors will be present. This may not be important in patients who do not require significant quantities of blood. Where it is not necessary to use the most recently donated blood, blood banks will send out older blood so as to minimise waste. However it has now become protocol in the US military to use the most recently donated blood for patients requiring massive transfusion. This has translated into civilian trauma care in the US and a special request for recently donated blood from the blood bank can be made when a patient in need of massive transfusion arrives at the emergency department.

In the US military, every soldier is aware of their blood type and therefore fresh whole blood can be donated on scene in emergency situations when component blood is unavailable.

Between March 2003 and July 2007, over 6000 units of warm fresh whole blood were transfused in Afghanistan and Iraq by US medical service providers to patients with life-threatening traumatic injuries with haemorrhage (23). Rapid screening assays are performed to ensure the blood is safe and free from infectious diseases. In patients who don’t stop bleeding despite all conventional treatments, fresh whole blood has frequently been seen to work. This is thought to be due to the fresh clotting factors. The effective use of fresh whole blood by the military has led to renewed interest in its use in civilian practice. Studies carried out on animals have had positive results, and human studies have shown that in emergency situations the risk: benefit ratio of fresh whole blood favours its use [23]][24]. Randomised trials are now being set up to determine whether the use of fresh whole blood could be favourable to that of component blood even when both are available.

In Ireland, individual hospitals each have separate protocols. However in general, patients requiring an emergency transfusion are initially administered a crystalloid, for example normal saline or Hartmann’s solution, and are then given colloid (plasma-type solutions) until the crossmatched blood becomes available. Alternatıvely these patients are gıven O-negative blood. Doctors attempt to keep blood pressure within normal limits - unlike the hypotensive resuscitation in the US - and keep haemoglobin greater than 8g/dL. After two litres of blood loss, fresh frozen plasma and platelets are given to replenish coagulation factors [25]. In time it is likely that protocols in Irish hospitals will evolve to incorporate aspects of damage control resuscitation, sound clinical judgement will be imperative in deciding when this should be used.

Identification of Patients who Require Damage Control Resuscitation

It is important to identify patients in need of damage control resuscitation as opposed to patients requiring ‘standard’ resuscitation because theoretically patients with less severe injuries could manifest hypercoagulability if subjected to DCR. This needs to be assessed quickly and is based on rapidly obtain- able clinical parameters. On the battlefield, approximately 95% of casualties present with penetrating injuries which has led to the identification of certain patterns of injury that reliably pre- dict the need for massive transfusion and DCR [26]. These patterns include patients with multiple proximal amputations (particularly thigh level), truncal haemorrhage combined with a proximal amputation and abdominal evisceration with hypotension [26]. Other measurable parameters which predict a need for DCR are: systolic blood pressure below 90 mmHg for a soldier or below 110 mmHg for a civilian, a base deficit of less than 6 mEq/L, a haemoglobin level of less than 11 g/dL, temperature of less than 35 degrees Celsius and a weak or absent radial pulse. Patients matching any of these clinical parameters should be immediately identified as in need of DCR. 

conclusion

Times of war have always precipitated innovations in medicine. One of the most important of these advances in the 21st century is the development of damage control resuscitation. DCR advises hypotensive resuscitation as opposed to conventional normotensive resuscitation and emphasises the importance of prevention and treatment of all three elements of the ‘trauma triad of death’. It is important to note that most data currently available concerning DCR is from retrospective observational studies and more definitive tests are needed to prove and further define the beneficial properties of DCR. Data analysis has been facilitated by the technological advances of the 20th and 21st centuries. The Trauma Audit and Research Network (TARN) actively produces evidence-based changes in treatment as result of auditing and research. There are elements in trauma management that require further research such as the use of fresh whole blood and the administration of exogenous bicarbonate or tris-hydroxymethyl aminomethane to reverse acidosis. With ongoing experimental work and data collection, the scientific community continues to improve the treatment of severe trauma injuries. 

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