Damage control resuscitation for patients with major trauma

What is the “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 (fig 1)⇓. Hypoperfusion leads to decreased oxygen delivery, a switch to anaerobic metabolism, lactate production, and metabolic acidosis. Anaerobic metabolism limits endogenous heat production, exacerbating hypothermia caused by exposure and injudicious administration of cold resuscitation fluids and blood. Large, well conducted retrospective studies have shown that a core temperature of less than 35°C on admission is an independent predictor of mortality after major trauma.3 ^w2

Fig 1 The “lethal triad” of acidosis, hypothermia, and coagulopathy

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Several observational studies have shown that around a quarter of trauma patients have an established, early coagulopathy on arrival in the emergency department, a finding associated with a four fold increase in mortality.4 5 6 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.7 8 9 Two prospective observational studies have shown that 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.7 8 The resulting haemostatic derangement is distinct from disseminated intravascular coagulation and has been termed acute coagulopathy of trauma-shock.9 An understanding of these underlying mechanisms forms the basis of haemostatic resuscitation.

What are the new strategies in trauma resuscitation?

Damage control resuscitation combines two seemingly diverse strategies—permissive hypotension and haemostatic resuscitation—with damage control surgery (fig 2⇓)2 ^{w3 w4} The foundation for this approach is set in the pre-hospital environment, where intravenous fluid administration is restricted to a volume sufficient to maintain a radial pulse.^w3 The term “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.2 4 Tranexamic acid, recombinant factor VIIa, and short term administration of tris(hydroxymethyl)aminomethane can also be used to “buy time”.

Fig 2 The components of damage control resuscitation

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Damage control resuscitation is designed to proceed hand in hand with damage control surgery. The sequential strategy of operation 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.

What is permissive hypotension?

During the second half of the 20th century, restoring normal circulatory function by aggressively replacing intravenous fluids was seen as pivotal in preventing haemorrhagic shock. Uncorrected haemorrhagic shock, the consequence of interrupted oxygen delivery as a result of blood loss, leads to cellular ischaemia, progressive organ dysfunction, and ultimately irreversible organ failure.

The recognition that fluid resuscitation might interfere with haemostatic mechanisms, ultimately exacerbating blood loss, led to a re-evaluation of this accepted approach. 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.

Proving the usefulness and safety of such an approach is beset by practical difficulties. A large nonrandomised trial conducted in the early 1990s showed a statistically significant 8% absolute reduction in mortality for hypotensive patients with penetrating torso trauma assigned to delayed (in the operating theatre) compared with pre-hospital or emergency room fluid resuscitation.10 Pre-hospital times were very short and patients in this study were mostly young; thus, extrapolating the findings to other settings or mechanisms of injury might not be appropriate. A cluster randomised trial of patients who had sustained mainly blunt trauma showed no difference in mortality between the delayed and immediate resuscitation groups, but included patients with relatively minor injuries and had many protocol violations, rendering the comparisons and conclusions meaningless.11 A third, smaller randomised trial of patients with either blunt or penetrating hypotensive trauma also showed no difference in mortality between controlled fluid resuscitation and conventional treatment,12 but again the study had considerable methodological shortcomings. These three trials were included in a Cochrane review—which also assessed two trials not pertaining to trauma patients—and a high quality systematic review, both of which showed no difference in mortality between early and delayed fluid administration.^{w5 w6}

No published evidence exists to support the strategy of permissive or controlled hypotension, although its usefulness has not been entirely ruled out either. Few would argue against replacing lost intravascular volume in patients with controlled or self limiting haemorrhage. In patients with uncontrolled haemorrhage, particularly in the context of penetrating torso trauma, a strategy of permissive hypotension, together with expert resuscitation and rapid control of haemorrhage, might be more appropriate. It is conceivable that permissive hypotension is more applicable to the management of penetrating trauma, which is often characterised by the presence of major vascular injuries, than to blunt injuries.

Despite the lack of evidence, guideline recommendations for clinical practice point towards judicious administration of intravenous fluids. In recognition of the unique challenges posed by combat casualties, permissive hypotension has been incorporated into military medical doctrine2 13 ^w7 and used widely during the recent conflicts in South West Asia. The National Institute for Health and Clinical Excellence has endorsed permissive hypotension in the civilian pre-hospital setting and advises against fluid administration in patients without head injury if a radial pulse is palpable.^w8 The forthcoming 8th 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.^w9

The management of polytrauma patients with head injuries requires special mention. The importance of maintaining cerebral perfusion pressure is well recognised; thus permissive hypotension is currently contraindicated in this setting.

What is haemostatic resuscitation and why perform it?

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.13 14 Strategies include: administration of fresh frozen plasma and platelets; use of recombinant factor VIIa, cryoprecipitate and tranexamic acid; and 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,13 14 so the decision to initiate clotting factor replacement is a clinical one.

How should I prevent and treat hypothermia?

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 easier than reversal, and the importance of mitigating heat loss is well appreciated. Strategies used to prevent hypothermia are summarised in box 1. Although little direct evidence exists for the efficacy of these measures, their application is rational and supported by a recent National Institute for Health and Clinical Excellence guideline on the management of perioperative hypothermia.^w23

How should I manage metabolic acidosis?

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 pathophysiological consequences of acidaemia on other organ systems, the coagulation system in particular. The traditional treatment for severe lactic acidosis in critical illness is sodium bicarbonate, but little rationale for its use and no evidence of its effectiveness in general, or in the trauma setting, is available.22 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.22 Tris(hydroxymethyl)aminomethane is a biologically inert amino alcohol capable of accepting hydrogen ions.23 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.

What is damage control surgery?

The concept of damage control surgery arose from the realisation that the massively traumatised patient lacked the physiological reserve to survive the rigours of complex and prolonged definitive or reconstructive surgery. The aim of damage control surgery is to stop haemorrhage and minimise contamination. Haemorrhage is controlled by temporary clamping, packing, shunting, or ligation, and hollow viscus injuries are either closed or resected without anastomosis.24 On completion of the procedure, the abdomen is temporarily closed using an improvised or commercially available topical negative pressure dressing, which saves time, helps to minimise the risk of intra-abdominal hypertension, and facilitates observation of the volume and nature of drainage from the abdomen.24 Planned re-operation to restore anatomy and achieve definitive repair is carried out on return to normal physiology. Damage control surgery is associated with potential morbidity and should be employed judiciously.

No randomised controlled trial has evaluated the concept of damage control surgery. A small study of patients with severe penetrating abdominal trauma showed a survival benefit for those treated with contemporary damage control techniques compared with historical controls (90% v 58%; P=0.02).^w4 A large non-systematic review published in 1997 reported an overall mortality of 50% and morbidity of 40% with damage control surgery, but the heterogeneity of patients and injuries and the lack of a control group make it difficult to draw meaningful conclusions from this study.25

Damage control surgery has nevertheless become an accepted part of the trauma surgeon’s armamentarium,24 but is now viewed as a component of damage control resuscitation. Damage control surgery should not be practised in isolation. The advances in damage control resuscitation techniques might in the future permit definitive surgical procedures, resulting in a decreased need for damage control surgery. At present, however, no data support this hypothesis.

Conclusion

Damage control resuscitation continues to evolve. Many of the concepts underlying this technique have come from meticulous evaluation of the process and outcome of military practice.1 Lessons learnt are now redefining the care of the most severely injured patients in civilian practice.