Abstract: - Damage Control Resuscitation (DCR) represents the natural evolution of the initial concept of Damage Control Surgery (DCS). The concept of DCR, which includes hypotensive and haemostatic resuscitation components, was introduced as a approach to treat those patients at the highest risk of dying. It currently includes early blood product transfusion, immediate arrest and/or temporization of ongoing haemorrhage as well as restoration of blood volume and physiologic/hematologic stability. DCR addresses the early coagulopathy of trauma, avoids massive crystalloid resuscitation and leaves definitive surgical intervention after stabilization. DCR concept also applies to severe injuries within anatomical transition zones as well as extremities. The aim of this presentation is to provide an overview of approach to managing major trauma by concept of DCR, and aims to address all aspects of the “lethal triad” immediately on receiving the injured patient.

01.       Introduction:
Damage control is a Navy term defined as “the capacity of a ship to absorb damage and maintain mission integrity.”  When applied to trauma surgery and critically ill patients, Damage Control Resuscitation (DCR) incorporates fundamental tenets: rewarming, correction of coagulopathy and hemodynamic stabilization. Definitive surgery is deferred with the recognition that patients are more likely to die from an uncorrected state of shock than from failure to complete organ repairs. The basic principles include arresting haemorrhage; restoring blood volume; and correcting coagulopathy, acidosis and hypothermia. Haemorrhage remains the leading cause of death in conventional warfare, accounting for about 50% of mortality on the battlefield and 30% of those who die of wounds after reaching a treatment facility. Current thinking dictates that early, adequate fluid resuscitation is crucial to reduce the mortality and morbidity associated with haemorrhagic shock. However, with future combat strategies focused around the Future Force Warrior, greater dispersal of troops and fighting in urban settings and on non-linear battlefields, the likelihood of longer evacuation times for combat casualties is anticipated. In military medicine, resuscitation practice will vary with the echelon of care. On the battlefield or during transportation, Tactical Combat Casualty Care (TCCC) guidelines recommend partial (hypotensive) resuscitation, the goal is to raise blood pressure enough to maintain oxygen delivery to tissue as measured by patient consciousness or discernible radial pulse. It is suggested not to raise mean arterial pressure (MAP) above 60 mmHg until haemorrhage control is achieved. Advanced Trauma Life Support (ATLS) guidelines call for a 3:1 volume replacement of lost blood with crystalloid solutions, followed serially, by packed red blood cells. In military situations, it is easy to envision a casualty developing a dilutional coagulopathy during prolonged evacuation periods. Also, it is now recognized that derangements in coagulation can occur rapidly as a consequence of traumatic injury itself. Recent data has shown all patients requiring massive transfusion were coagulopathic on admission to a Combat Support Hospital (CSH). DCR at the CSH/ Field Hospitals focuses on avoiding further dilution of coagulation factors in the sickest patients with the highest risk of dying, by using appropriate blood products and limiting the amount of crystalloids.
02.       Military Conflict & DCR:                                                                                     Military conflict has always driven innovation and technical advances in medicine and surgery. Accepted concepts of trauma resuscitation and surgery have been challenged in recent military conflict zones. Advances in trauma management has almost certainly contributed to a remarkable reduction in the lethality of war wounds. Only 10% of United States servicemen wounded in Iraq and Afghanistan between 2003 and 2009 died, compared with 24% in the first Gulf War(1990-1991) and Vietnam War(1961-1973). Many of these advances are also relevant to trauma care in civilian practice.  
03.       Lethal Triad:
The term “Lethal Triad” is used to describe the mutually perpetuating combination of acute coagulopathy, hypothermia, and acidosis seen in exsanguinating trauma patients. Hypoperfusion leads to decreased oxygen delivery, a switch to anaerobic metabolism, lactate production, and metabolic acidosis. Anaerobic metabolism limits endogenous heat production & exacerbating hypothermia. A core temperature of less than 35°C on admission is an independent predictor of mortality after major trauma. Coagulopathy was classically considered to be the product of procoagulant protease losses (a result of consumption and bleeding), dilution (due to fluid resuscitation), and dysfunction (related to acidosis and hypothermia). Recent research, however, has shown that the pathophysiology of coagulopathy is more complex. Hypoperfusion is an important driver of early post-injury coagulopathy, although tissue injury is the initiating event. In addition, both anticoagulation and hyperfibrinolysis appear to contribute to coagulopathy. The resulting haemostatic derangement is distinct from disseminated intravascular coagulation and has been termed “Acute Coagulopathy of Traumatic Shock”. An understanding of these underlying mechanisms forms the basis of haemostatic resuscitation.

04.       New strategies in Trauma Resuscitation:
DCR combines two diverse strategies i.e. Permissive Hypotension and Haemostatic Resuscitation along with DCS. In the pre-hospital environment, intravenous fluid administration is restricted to a volume sufficient to maintain a radial pulse. “Haemostatic Resuscitation” describes the very early use of blood and blood products as primary resuscitation fluids, to treat intrinsic acute traumatic coagulopathy and to prevent the development of dilutional coagulopathy. Along with the above Tranexamic acid, recombinant factor VIIa and short term administration of Tris(hydroxymethyl)aminomethane can also be used to “buy time”. DCR is designed to proceed hand in hand along with DCS. The sequential strategy of surgery followed by resuscitation has been replaced by an integrated approach so that resuscitation and surgery are undertaken simultaneously, with close communication and cooperation between surgeon and anaesthetist.

05.       Permissive Hypotension:
Permissive hypotension, also known as “hypotensive” or “balanced” resuscitation, is a strategy of deferring or restricting fluid administration until haemorrhage is controlled, while accepting a limited period of suboptimum end-organ perfusion. It is more applicable to the management of penetrating trauma than to blunt injuries. In recognition of the unique challenges posed by combat casualties, permissive hypotension has been incorporated into military medical doctrine and used widely during the recent conflicts in South West Asia. Eight edition of the Advanced Trauma Life Support programme also emphasises the need to balance the risk of precipitating further bleeding against the adequacy of organ perfusion by accepting a lower than normal blood pressure. Permissive hypotension is currently contraindicated in the management of polytrauma patients with head injuries so as to not compromise cerebral perfusion pressure (CPP).

06.       Haemostatic Resuscitation:
Although aggressive and simultaneous management of all three aspects of the “Lethal Triad” is important, rapid and proactive treatment of the coagulopathy associated with major injury is now recognised as central to improving outcome.
The various strategies for achieving the same include:

1. Administration of Fresh Frozen Plasma and Platelets
2. Use of recombinant factor VIIa
3. Cryoprecipitate
4. Tranexamic acid
5. Calcium replacement

The high prevalence and profound impact of coagulopathy mandates timely treatment of trauma patients. Commonly available diagnostic tests, such as Prothrombin Time and activated Partial Thromboplastin Time, are inappropriate for guiding treatment in trauma patients owing to their poor sensitivity and the delay in obtaining results. Hence the decision to initiate clotting factor replacement remains largely a clinical one.

07.       Role of Fresh Frozen Plasma:
In patients predicted to require massive transfusion, current global military medicine practice is to administer fresh frozen plasma and packed red blood cells in a 1:1 ratio. Aggressive and early administration of fresh frozen plasma to attenuate the acute coagulopathy of trauma shock was pioneered by military surgeons during the recent conflict in Iraq. Studies have shown a statistically significant absolute reduction in mortality (46%) for those who had been resuscitated with fresh frozen plasma and packed red blood cells in a 1:1 ratio compared with a more conventional 1:8 ratio in military casualties who needed massive transfusion.

08.       Role of Platelets:
Military guidelines for haemorrhagic shock also recommend the administration of platelets in a 1:1 ratio with packed red blood cells. The administration of platelets and packed red blood cells in combination with a 1:1 ratio of fresh frozen plasma and packed red blood cells approximates giving whole blood. This approach is conceptually attractive but based on limited evidence. The effect of high platelet to packed cell ratios has only been investigated in two retrospective observational studies which showed improved survival with a 1:1 ratio compared with lower ratios. More studies are needed before firm recommendations can be made.

09.       Role of Factor VIIa?
The importance of trauma related coagulopathy has prompted a search for pharmacological adjuncts to treatment. Recombinant factor VIIa is licensed for use in patients with haemophilia and inhibitory antibodies.  Over the past few years, it has been used "off-label" in patients with uncontrolled bleeding due to trauma and/or massive blood loss, thrombocytopenia, platelet dysfunction or liver dysfunction. Factor VII is a crucial initial component of the coagulation cascade and thought to enhance local haemostasis at the site of injury. Studies have shown a statistically significant reduction in blood transfusion requirements in patients treated with recombinant factor VIIa with blunt, but not penetrating trauma. In view of the substantial cost of the product, further studies, in particular economic analyses, are needed.

10.       Role of Fibrinogen Concentrate/ Cryoprecipitate:
In traumatic coagulopathy patients, Fibrinogen deficiency develops earlier than of other clotting factors. Fibrinogen is, therefore, an obvious target for replacement with either cryoprecipitate—which contains fibrinogen, factor VIII, factor XIII, and von Willebrand factor—or fibrinogen concentrate. British and European guidelines recommend giving either product if plasma fibrinogen levels fall below 1.0 g/l. However the grave concerns about patient exposure to a large number of donors and potential, associated risk of blood borne virus transmission limit the use of cryoprecipitate to situations where conventional treatment has failed.

11.       Role of Tranexamic Acid:
The recognition of the contribution of hyperfibrinolysis to the development of acute coagulopathy in trauma shock has led to renewed interest in antifibrinolytics. Although tranexamic acid has been shown to reduce blood loss after elective surgery, there exists insufficient evidence to support or refute routine use. However on the basis of extrapolated evidence from studies of elective surgery, and lack of serious adverse effects, European guidelines for the management of bleeding after major trauma recommend tranexamic acid as an adjunct to the management  of traumatic haemorrhage.

12.       Role of Calcium:
Ionised hypocalcaemia is common in massive traumatically, critical patients and is associated with increased mortality. Calcium is an important cofactor to many components of the coagulation cascade. Citrate, used as an anticoagulant in many blood components, chelates calcium and exacerbates hypocalcaemia. The dose response effect of hypocalcaemia on coagulation is difficult to measure. Calcium concentrations of less than 0.6-0.7 mmol/l could lead to coagulation defects. It is recommended to maintain a concentration of at least 0.9mmol/l.

13.       Storage age Of PRBC’s:
The transfusion of red cells with a high storage age has been associated with increased rates of infective complications and multiple organ failure. Although the shelf life of packed red cell units is around six weeks, adverse effects of administration, which are thought to be mediated by leukocytes, have been shown with units at a storage age of about two weeks. Transfusion of red cells (> 6 pack units) stored for longer than two weeks was associated with significantly increased odds of death despite leukoreduction. Recently donated red cells (< 2 weeks) are, therefore, preferable for trauma patients requiring massive transfusion.

14.       Hypothermia & DCR:
The detrimental effects of hypothermia on coagulation, platelet function, and metabolism are well recognised. Major injury directly leads to reduced production of body heat. Prevention of hypothermia, is therefore easier than reversal, and the importance of mitigating heat loss is well appreciated. Strategies used to prevent hypothermia are:

1. Limit casualties’ exposure to ambient temperature
2. Warm all blood products and intravenous fluids before administration
3. Use forced air warming devices, which are useful before and after surgery but are less effective when the need for operative exposure restricts application to the limbs
4. Employ carbon polymer heating mattresses, which are highly effective and do not restrict surgical access, and are, therefore, the device of choice for the operating theatre

  15.       Metabolic Acidosis & DCR:
Metabolic acidosis associated with haemorrhagic shock is a product of      hypoperfusion. Although correction of metabolic acidosis requires restoration of organ perfusion, volume replacement may need to be deferred until haemorrhage has been controlled. This requirement has led to a search for adjunctive pharmacological treatments to offset the patho-physiological consequences of acidaemia on other organ systems including coagulation system in particular. There is no evidence for use of sodium bicarbonate in settings of trauma for treatment of severe lactic acidosis. The administration of sodium bicarbonate produces carbon dioxide, which can require large increases in minute volume to clear. In addition, sodium bicarbonate decreases ionised calcium concentrations by about 10%, which has deleterious effects on coagulation and cardiac and vascular contractility.

16.       What’s New?
Tris(hydroxymethyl)aminomethane is a biologically inert amino alcohol capable of accepting hydrogen ions. Clinical experience with this product in trauma patients is limited and the precise role of tris (hydroxymethyl)aminomethane in trauma resuscitation is yet to be defined, although the possible applications are attractive in theory.

17.       Conclusion:
The military   has shared man’s eternal quest to make possible the humane treatment of survivors of trauma. Military and civilian anaesthesia providers have learned from each other strategies to promote the treatment of the seriously injured patient. DCR continues to evolve with more research and advances in war/ trauma surgery. Many of the concepts underlying this technique have come from meticulous evaluation of the process and outcome of military practice. These lessons learnt are now redefining the care of the most severely injured patients in civilian practice.