Clot Stabilization for the Prevention of Bleeding

Platelet dysfunction in injured patients

A renewed understanding of Trauma Induced Coagulopathy (TIC) has implicated platelets as a crucial mediator and potential therapeutic target in hemostasis. While the importance of abnormal coagulation tests is well described in trauma, there is a paucity of data regarding the role of platelets in coagulopathy. New coagulation models, namely the cell-based-model of hemostasis, have refocused attention toward the platelet and endothelium as key regulators of clot formation. Although platelet dysfunction has been associated with worse outcomes in trauma, the mechanisms which platelet dysfunction contributes to coagulopathy are poorly understood. The goal of this review article is to outline recent advances in understanding hemostasis and the ensuing cellular dysfunction that contributes to the exsanguination of a critically injured patient.

Platelet dysfunction in injured patients

A renewed understanding of Trauma Induced Coagulopathy (TIC) has implicated platelets as a crucial mediator and potential therapeutic target in hemostasis. While the importance of abnormal coagulation tests is well described in trauma, there is a paucity of data regarding the role of platelets in coagulopathy. New coagulation models, namely the cell-based-model of hemostasis, have refocused attention toward the platelet and endothelium as key regulators of clot formation. Although platelet dysfunction has been associated with worse outcomes in trauma, the mechanisms which platelet dysfunction contributes to coagulopathy are poorly understood. The goal of this review article is to outline recent advances in understanding hemostasis and the ensuing cellular dysfunction that contributes to the exsanguination of a critically injured patient.

Formation of blood clot on biomaterial implants influences bone healing

The first step in bone healing is forming a blood clot at injured bones. During bone implantation, biomaterials unavoidably come into direct contact with blood, leading to a blood clot formation on its surface prior to bone regeneration. Despite both situations being similar in forming a blood clot at the defect site, most research in bone tissue engineering virtually ignores the important role of a blood clot in supporting healing. Dental implantology has long demonstrated that the fibrin structure and cellular content of a peri-implant clot can greatly affect osteoconduction and de novo bone formation on implant surfaces. This article reviews the formation of a blood clot during bone healing in relation to the use of platelet-rich plasma (PRP) gels. It is implicated that PRP gels are dramatically altered from a normal clot in healing, resulting in conflicting effect on bone regeneration. These results indicate that the effect of clots on bone regeneration depends on how the clots are formed. Factors that influence blood clot structure and properties in relation to bone healing are also highlighted. Such knowledge is essential for developing strategies to optimally control blood clot formation, which ultimately alter the healing microenvironment of bone. Of particular interest are modification of surface chemistry of biomaterials, which displays functional groups at varied composition for the purpose of tailoring blood coagulation activation, resultant clot fibrin architecture, rigidity, susceptibility to lysis, and growth factor release. This opens new scope of in situ blood clot modification as a promising approach in accelerating and controlling bone regeneration.

Tranexamic acid corrects fibrinolysis in the presence of acidemia in a swine model of severe ischemic reperfusion

BACKGROUND

Tranexamic acid (TXA) is an antifibrinolytic with anti-inflammatory properties associated with improved outcomes when administered to trauma patients at risk for bleeding; however, its efficacy is unknown in acidemia. We evaluated the efficacy of TXA on hyperfibrinolysis using an established porcine traumatic hemorrhage ischemic shock model.

METHODS

Ten Yorkshire swine underwent a controlled hemorrhage followed by supraceliac aortic cross-clamping. During standard resuscitation, control animals received recombinant tissue plasminogen activator (rtPA) after cross-clamp removal, and experimental animals received rtPA followed by TXA. Rotational thromboelastometry analysis was performed at baseline, 5 minutes and 15 minutes after rtPA dosing, and 4 hours after cross-clamp removal.

RESULTS

Control and experimental animals had similar hemodynamics and routine laboratory values at baseline and throughout resuscitation. At the time of TXA administration, average pH was 7.2. Clot formation time was prolonged from baseline and all resuscitation time points in both groups, with no difference at any time point. Maximum clot firmness decreased from baseline at all resuscitation time points in both groups. Maximum lysis increased from baseline (9% control vs. 9% TXA) after tissue plasminogen activator administration in both groups (100% control vs. 99% TXA). In experimental animals, maximum lysis returned to baseline 10 minutes after TXA administration (92% vs. 9%, p < 0.001).

CONCLUSION

TXA rapidly and fully reverses hyperfibrinolysis despite severe acidemia in a porcine trauma model. TXA is a promising adjunct to trauma resuscitation that is easily administered in austere or prehospital settings.

Emerging treatment strategies for trauma-induced coagulopathy

Background

Trauma-induced coagulopathy has a multifactorial aetiology. Coagulopathy is related to blood loss including consumption of clotting factors and platelets and haemodilution. Additionally hyperfibrinolysis, hypothermia, acidosis and metabolic changes affect the coagulation system.

Methods

This is a review of pathophysiology and new treatment strategies for trauma-induced coagulopathy.

Results

Paradigms are actively changing and there is still a shortage of data. The aim of any haemostatic therapy is to control bleeding and minimize blood loss and transfusion requirements. Transfusion of allogeneic blood products as well as trauma-induced coagulopathy cause increased morbidity and mortality. Current opinion is based on present studies and results from small case series, combined with findings from experimental studies in animals, in vitro studies and expert opinions, as opposed to large, randomized, placebo-controlled studies. A summary of new and emerging strategies, including medical infusion and blood products, to beneficially manipulate the coagulation system in the critically injured patient is suggested.

Conclusion

Future treatment of trauma-induced coagulopathy may be based on systemic antifibrinolytics, local haemostatics and individualized point-of-care-guided rational use of coagulation factor concentrates such as fibrinogen, prothrombin complex concentrate, recombinant factor VIIa and factor XIII. The authors speculate that timely and rational use of coagulation factor concentrates will be more efficacious and safer than ratio-driven use of transfusion packages of allogeneic blood products.

Thrombelastography and biomarker profiles in acute coagulopathy of trauma: a prospective study

BACKGROUND

Severe injury induces an acute coagulopathy associated with increased mortality. This study compared the Thrombelastography (TEG) and biomarker profiles upon admission in trauma patients.

METHODS

Prospective observational study of 80 trauma patients admitted to a Level I Trauma Centre. Data on demography, biochemistry including standard coagulation tests, hematology, transfusions, Injury Severity Score (ISS) and TEG were recorded. Retrospective analysis of thawed plasma/serum for biomarkers reflecting tissue injury (histone-complexed DNA fragments), sympathoadrenal activation (adrenaline, noradrenaline), coagulation activation/inhibition and fibrinolysis (sCD40L, protein C, activated Protein C, tissue-type plasminogen activator, plasminogen activator inhibitor-1, D-dimer, prothrombinfragment 1+2, plasmin/α2-antiplasmin complex, thrombin/antithrombin complex, tissue factor pathway inhibitor, antithrombin, von willebrand factor, factor XIII). Comparison of patients stratified according to ISS/TEG maximum clot strength. Linear regression analysis of variables associated with clot strength.

RESULTS

Trauma patients had normal (86%), hypercoagulable (11%) or hypocoagulable (1%) TEG clot strength; one had primary hyperfibrinolysis. Hypercoagulable patients had higher age, fibrinogen and platelet count (all p < 0.05), none had increased activated partial thromboplastin time (APTT) or international normalized ratio (INR) and none required massive transfusion (> 10 red blood cells the initial 24 h). Patients with normal or hypercoagulable TEG clot strength had comparable biomarker profiles, but the few patients with hypocoagulable TEG clot strength and/or hyperfibrinolysis had very different biomarker profiles.Increasing ISS was associated with higher levels of catecholamines, histone-complexed DNA fragments, sCD40L, activated protein C and D-dimer and reduced levels of non-activated protein C, antithrombin, fibrinogen and factor XIII (all p < 0.05). Fibrinogen and platelet count were associated independently with clot strength in patients with ISS ≤ 26 whereas only fibrinogen was associated independently with clot strength in patients with ISS > 26. In patients with ISS > 26, adrenaline and sCD40L were independently negatively associated with clot strength.

CONCLUSIONS

Trauma patients displayed different coagulopathies by TEG and variables independently associated with clot strength changed with ISS. In the highest ISS group, adrenaline and sCD40L were independently negatively associated with clot strength indicating that these may contribute to acute coagulopathy.

Differential clot stabilising effects of rFVIIa and rFXIII-A2 in whole blood from thrombocytopenic patients and healthy volunteers

The haemostatic effect of recombinant activated factor VII (rFVIIa;NovoSeven) in thrombocytopenic patients has been a matter of controversy. Haemostasis by rFVIIa occurs via FVIIa-mediated thrombin generation in a platelet-dependent manner and may therefore be suboptimal in patients without functional platelets. Under such conditions, a clot-stabilizing agent, such as factor XIII (FXIII), may supplement the effect ofrFVIIa and improve haemostasis. Recombinant factor XIII (rFXIII-A2) is produced as an A2 homodimer of the FXIII A subunit and is equivalent to cellular FXIII normally found in platelets. The combined effects of rFVIIa andrFXIII-A2 were evaluated in clot lysis assays using factor XIII-deficient plasma and by whole blood thrombelastography (TEG) analysis from normal donors and thrombocytopenic stem cell transplantation patients. Clotting time was shortened by rFVIIa (0.6-10 microg/ml). rFVIIa only modestly improved anti-fibrinolysis,whereas rFXIII-A2 (0-20 microg/ml) enhanced anti-fibrinolysis without effect on clotting time. TEG analysis showed rFVIIa shortened the clotting time, and enhanced clot development, maximal mechanical strength and resistance to fibrinolysis, whereas, rFXIII-A2 enhanced clot development,maximal mechanical strength and markedly enhanced resistance to fibrinolysis. These data illustrate that rFVIIa and rFXIII-A2 contribute to clot formation and stability by different mechanisms suggesting enhanced haemostatic efficacy by combining these agents.