Claire Rourke

Fibrinogen levels during trauma hemorrhage, response to replacement therapy, and association with patient outcomes

Summary.  Background:  Low fibrinogen levels are known to occur in trauma. However, the extent of fibrinogen depletion during trauma hemorrhage, the response to replacement therapy and association with patient outcomes remain unclear.

The incidence and magnitude of fibrinolytic activation in trauma patients

Summary.  Background: Trauma is a global disease, with over 2.5 million deaths annually from hemorrhage and coagulopathy. Overt hyperfibrinolysis is rare in trauma, and is associated with massive fatal injuries. Paradoxically, clinical trials suggest a much broader indication for antifibrinolytics.

Hemostatic effects of fresh frozen plasma may be maximal at red cell ratios of 1:2.

BACKGROUND Damage control resuscitation targets acute traumatic coagulopathy with the early administration of high-dose fresh frozen plasma (FFP). FFP is administered empirically and as a ratio with the number of packed red blood cells (PRBC). There is controversy over the optimal FFP:PRBC ratio with respect to outcomes, and their hemostatic effects have not been studied. We report preliminary findings on the effects of different FFP:PRBC ratios on coagulation. METHODS This is a prospective observational cohort study of trauma patients requiring >4 U of PRBCs. Blood was drawn before and after each 4-U PRBC interval for prothrombin time and analysis by rotational thromboelastometry. Interval change in coagulation parameters were compared with the FFP:PRBC ratio received during each interval. RESULTS Sixty 4-U PRBC intervals from 50 patients were available for analysis. All measures of coagulation deteriorated with low FFP:PRBC ratios (<1:2). Maximal hemostatic effect was observed in the 1:2 to 3:4 group: 12% decrease in prothrombin time (p=0.006), 56% decrease in clotting time (p=0.047), and 38% increase in maximum clot firmness (p=0.024). Transfusion with ≥1:1 ratio did not confer any additional improvement. There was a marked variability in response to FFP, and hemostatic function deteriorated in some patients exposed to 1:1 ratios. The beneficial effects of plasma were confined to patients with coagulopathy. CONCLUSIONS Interim results from this prospective study suggest that FFP:PRBC ratios of ≥1:1 do not confer any additional advantage over ratios of 1:2 to 3:4. Hemostatic benefits of plasma therapy are limited to patients with coagulopathy.

Leukotriene B4-Neutrophil Elastase Axis Drives Neutrophil Reverse Transendothelial Cell Migration In Vivo.

Summary Breaching endothelial cells (ECs) is a decisive step in the migration of leukocytes from the vascular lumen to the extravascular tissue, but fundamental aspects of this response remain largely unknown. We have previously shown that neutrophils can exhibit abluminal-to-luminal migration through EC junctions within mouse cremasteric venules and that this response is elicited following reduced expression and/or functionality of the EC junctional adhesion molecule-C (JAM-C). Here we demonstrate that the lipid chemoattractant leukotriene B4 (LTB4) was efficacious at causing loss of venular JAM-C and promoting neutrophil reverse transendothelial cell migration (rTEM) in vivo. Local proteolytic cleavage of EC JAM-C by neutrophil elastase (NE) drove this cascade of events as supported by presentation of NE to JAM-C via the neutrophil adhesion molecule Mac-1. The results identify local LTB4-NE axis as a promoter of neutrophil rTEM and provide evidence that this pathway can propagate a local sterile inflammatory response to become systemic.

Early cryoprecipitate for major haemorrhage in trauma: a randomised controlled feasibility trial

BACKGROUND Low fibrinogen (Fg) concentrations in trauma haemorrhage are associated with poorer outcomes. Cryoprecipitate is the standard source for Fg administration in the UK and USA and is often given in the later stages of transfusion therapy. It is not known whether early cryoprecipitate therapy improves clinical outcomes. The primary aim of this feasibility study was to determine whether it was possible to administer cryoprecipitate, within 90 min of admission to hospital. Secondary aims were to evaluate laboratory measures of Fg and clinical outcomes including thrombotic events, organ failure, length of hospital stay and mortality. METHODS This was an unblinded RCT, conducted at two civilian UK major trauma centres of adult trauma patients (age ≥16 yrs), with active bleeding and requiring activation of the major haemorrhage protocol. Participants were randomised to standard major haemorrhage therapy (STANDARD) (n=22), or to standard haemorrhage therapy plus two early pools of cryoprecipitate (CRYO) (n=21). RESULTS 85% (95% CI: 69-100%) CRYO participants received cryoprecipitate within 90 min, median time 60 min (IQR: 57-76) compared with 108 min (67-147), CRYO and STANDARD arms respectively (P=0.002). Fg concentrations were higher in the CRYO arm and were maintained above 1.8 g litre(-1) at all time-points during active haemorrhage. All-cause mortality at 28 days was not significantly different (P=0.14). CONCLUSIONS Early Fg supplementation using cryoprecipitate is feasible in trauma patients. This study supports the need for a definitive RCT to determine the effect of early Fg supplementation on mortality and other clinical outcomes. TRIAL REGISTRY NUMBER ISRCTN55509212.

Activated Protein C Drives the Hyperfibrinolysis of Acute Traumatic Coagulopathy.

Background: Major trauma is a leading cause of morbidity and mortality worldwide with hemorrhage accounting for 40% of deaths. Acute traumatic coagulopathy exacerbates bleeding, but controversy remains over the degree to which inhibition of procoagulant pathways (anticoagulation), fibrinogen loss, and fibrinolysis drive the pathologic process. Through a combination of experimental study in a murine model of trauma hemorrhage and human observation, the authors’ objective was to determine the predominant pathophysiology of acute traumatic coagulopathy. Methods: First, a prospective cohort study of 300 trauma patients admitted to a single level 1 trauma center with blood samples collected on arrival was performed. Second, a murine model of acute traumatic coagulopathy with suppressed protein C activation via genetic mutation of thrombomodulin was used. In both studies, analysis for coagulation screen, activated protein C levels, and rotational thromboelastometry (ROTEM) was performed. Results: In patients with acute traumatic coagulopathy, the authors have demonstrated elevated activated protein C levels with profound fibrinolytic activity and early depletion of fibrinogen. Procoagulant pathways were only minimally inhibited with preservation of capacity to generate thrombin. Compared to factors V and VIII, proteases that do not undergo activated protein C–mediated cleavage were reduced but maintained within normal levels. In transgenic mice with reduced capacity to activate protein C, both fibrinolysis and fibrinogen depletion were significantly attenuated. Other recognized drivers of coagulopathy were associated with less significant perturbations of coagulation. Conclusions: Activated protein C–associated fibrinolysis and fibrinogenolysis, rather than inhibition of procoagulant pathways, predominate in acute traumatic coagulopathy. In combination, these findings suggest a central role for the protein C pathway in acute traumatic coagulopathy and provide new translational opportunities for management of major trauma hemorrhage.

Clinical and biomarker profile of trauma-induced secondary cardiac injury

Secondary cardiac injury has been demonstrated in critical illness and is associated with worse outcomes. The aim of this study was to establish the existence of trauma‐induced secondary cardiac injury, and investigate its impact on outcomes in injured patients.

Fibrinogen replacement in trauma haemorrhage

There is a growing interest in the role that fibrinogen plays in major haemorrhage. It has been known since 1995 that fibrinogen is one of the first coagulation proteins to fall to critically low levels during major blood loss [1], but the clinical relevance of this is only now being evaluated. Injury is the leading cause of death worldwide for patients aged 1-45 and accounts for 7,800 deaths in UK annually. Uncontrolled haemorrhage is the most common treatable cause of death in this population; four out of every ten trauma patients die as a result of exsanguination, or its late effects. Most trauma deaths from haemorrhage occur within the first six hours of hospital admission and early control of bleeding may have a significant impact on mortality. By increasing understanding of the precipitants of uncontrolled bleeding (i.e. acute traumatic coagulopathy) and targeting therapy accordingly, it is expected that major haemorrhage therapy and more importantly, clinical outcomes, can be further improved. This short review briefly evaluates what is known about fibrinogen during major trauma haemorrhage, focusing on the changes that take place during traumatic coagulopathy and the role that fibrinogen supplementation may play in treatment of trauma haemorrhage. Transfusion therapy is an integral and costly part of supportive treatment for major blood loss. A large UK epidemiological study of patients with traumatic haemorrhage reported the annual cost to the NHS of treating major haemorrhage was £168 million (2012 prices) (NIHR PGfAR: ‘Traumatic Coagulopathy & Massive Transfusion: Improving Outcomes & Saving Blood, 2013). Early haemorrhage control may reduce this cost but high quality evidence evaluating transfusion practice for trauma haemorrhage is lacking. The results of a recently completed North American study, PROPPR (NCT01545232) which evaluated the effect of different ratios of blood components (1:1:1 vs. 1:1:2 - FFP: platelets:RBC) on mortality in 680 trauma patients are eagerly awaited. Thrombosis, as an appropriate response to bleeding, is critically dependent on fibrinogen. Fibrinogen is cleaved and activated by thrombin to produce insoluble fibrin strands which form the basis of a stable clot. Fibrinogen also acts as the ligand for platelet aggregation, thus localising platelets to a developing clot. FXIIIa then modifies the fibrin matrix by binding to, and cross-linking, fibrin strands and this leads to stabilisation and increased resistance of the clot to fibrinolysis (FXIIIa covalently binds alpha-2 anti-plasmin to fibrinogen). Fibrinogen levels fall early during major haemorrhage reflecting many on-going processes, including: factor consumption, dilution (as a result of fluid therapy), fibrinolysis and fibrinogenolysis. Increased fibrinolysis has been shown to be a major component of acute traumatic coagulopathy [2] and is likely due to both the high levels of free tPA released immediately after injury and the inhibition of PAI-1 by activated protein C; resulting in increased plasmin generation and clot degradation. Moreover, the effects of fibrinolysis are likely exacerbated in trauma haemorrhage by low fibrinogen levels, since fibrin strands formed in a hypofibrinogenaemic environment are more susceptible to lysis. These changes in fibrinolysis have now been tested in a large trial of tranexamic acid [3]. Hypofibrinogenaemia has been shown to be an important component of traumatic coagulopathy [4]. A recent prospective analysis of 517 trauma patients demonstrated that coagulopathic patients had significantly lower fibrinogen levels (1.6 g/L vs. 2.4 g/L; p < 0.001) upon arrival in the emergency department compared to non-coagulopathic patients [5]. Fibrinogen levels fell in association with rising base deficit; falling systolic blood pressure and high injury severity (ISS ≥ 25). The same group also demonstrated that the presence of hypofibrinogenaemia (i.e. < 1.5 g/L) at hospital admission was an independent predictor of mortality, both at 24 hours and 28 days [5]. Furthermore, for those patients with coagulopathy, ex vivo addition of therapeutic concentrations of fibrinogen (in the form of cryoprecipitate or fibrinogen concentrate(FgC)), led to ‘reversal’ of acute traumatic coagulopathy as defined by ROTEM measurements, providing early evidence that fibrinogen supplementation may be of clinical benefit in trauma haemorrhage. There are clinical data to suggest that fibrinogen supplementation may improve outcomes for trauma haemorrhage; by reducing blood loss and increasing survival. Three observational studies have reported improved survival with higher fibrinogen:RBC transfusion ratios in trauma. In an uncontrolled observational trauma study of 131 haemorrhagic patients, mortality rates were reported to fall by 14% after FgC treatment. Data outside trauma also support the use of fibrinogen supplementation for acquired bleeding. A small randomised placebo-controlled cardiac study has confirmed that FgC can significantly reduce (2 units vs. 13 units, p = < 0.001) total numbers of allogeneic blood components transfused (RBC, FFP & platelets), when administered using a ROTEM algorithm (NCT00701142). A recent systematic review appraising the management of major bleeding in trauma and focusing on transfusion therapy, found no high quality data supporting a safe and effective fibrinogen level and found no completed trauma RCTs evaluating the effect of FgC or cryoprecipitate [6]. Similarly, a Cochrane review evaluating FgC therapy highlighted inadequacies in the current published RCT literature; most studies were small and of poor methodological quality [7]. The current standard source of fibrinogen in UK is cryoprecipitate but fibrinogen concentrate (FgC) is increasingly being used in Europe and there is a growing interest in its use in UK. Cryoprecipitate (a pooled blood component derived from whole blood donation) has a variable but high fibrinogen concentration (15-20 g/L) and contains additional coagulation factors (FVIII, FXIII, fibronectin, von Willebrand factor), which may further contribute to haemostasis. Cryoprecipitate requires thawing in a controlled environment prior to transfusion, a process which takes approximately 20 minutes. FgC (Riastap™) has been used for many years for the treatment of inherited dys-/hypo-fibrinogenaemia and has a good safety profile. It is not licensed in UK for acquired bleeding disorders, such as major haemorrhage. Riastap™ is a plasma product with standardised fibrinogen content (20 g/L); is subjected to viral inactivation (pasteurisation-heat treatment at +60°C for 20 hours); and can be reconstituted at the bedside. The cost per gram of fibrinogen in cryoprecipitate is £85 (2013 prices) compared to £400 for fibrinogen concentrate. RCT evidence is urgently required to provide much needed answers to questions, such as: does early fibrinogen supplementation improve clinical outcomes in trauma haemorrhage; what dose of fibrinogen should be administered; and which method of fibrinogen replacement (FgC or cryoprecipitate) is more effective? A small UK RCT (CRYOSTAT – ISRCTN55509212), evaluating the feasibility of transfusing cryoprecipitate to trauma patients within 90 minutes of randomisation, has recently been completed. There is one other on-going RCT (NCT01475344) in trauma which is evaluating the effects of FgC on laboratory measures of fibrinogen (FIBTEM), and may provide data which can guide fibrinogen dosing in major blood loss. It is hoped that the preliminary data from pilot or feasibility studies will support and inform the optimal design of a larger RCT, evaluating the effects of cryoprecipitate or FgC therapy on mortality and bleeding outcomes. But, RCTs evaluating mortality endpoints require large numbers of participants and studies of this size require collaboration on a national or even international scale. This will be an on-going challenge, but one that must be overcome, if definitive trauma studies with relevant clinical endpoints (e.g. mortality) are to be successfully completed.

Time course of lactate clearance in trauma and its relevance to outcomes

Serum lactate is raised during haemorrhage of trauma and high admission levels are associated with worse outcomes. The time-course of lactate clearance and the effect of packed red blood cell transfusion (PRBC) has not previously been described. This information is important for clinical trials of novel oxygen therapeutics.

Thromboelastometry diagnosed Acute Traumatic Coagulopathy (ATC) identifies trauma patients with poor clinical outcomes better than Disseminated Intravascular Coagulation (DIC) scoring

Acute Traumatic Coagulopathy and Disseminated Intravascular coagulation are two definitions currently used to describe the endogenous hemostatic impairment that occurs early after injury. They have separate diagnostic criteria and different putative pathophysiology. The aim of this study was to determine which system better identifies trauma patients with high morbidity and mortality. A prospective observational cohort study was performed at a level 1 trauma center. Blood was collected on arrival in the emergency department (ED) from all adult trauma patients who met the local criteria for full trauma team activation. Exclusion criteria included ED arrival >2 hours after injury or >2000mL of fluid before arrival. Blood was analysed by routine laboratory coagulation tests, rotational thromboelastometry and ELISA. Contingency analysis was performed by Fishers exact test. Four hundred and thirty patients were included in the study. Seventy-six (18%) attended with ATC, as defined by EXTEM CA5 ţ 35mm. Laboratory coagulation results for DIC scoring were available at a median of 78 (62-103) mins. Eighteen (4%, p<0.001) met criteria for DIC on arrival using the amended ISTH scoring system. Of note, 86% of patients had elevated d-dimers without any scoring abnormality of prothrombin time, fibrinogen or platelets. Overall, 115 patients required a blood transfusion within the first 12 hours. Thirty-seven (32%) of these met RoTEM criteria for ATC on admission but only fourteen (12%) had DIC (p<0.001). Similarly, 106 patients experienced a septic episode; 26% had ATC on admission but only 4% had DIC (p<0.001). Forty-seven patients died, 45% of whom had ATC on admission compared with 32% that could be diagnosed with DIC (p=0.2). Although the pathophysiology of ATC remains to be fully elucidated, this study indicates that RoTEM diagnosis is more sensitive and clinically useful than DIC scoring criteria for the early identification of trauma patients with poor outcomes.