Disseminated intravascular coagulation: an update on pathogenesis and diagnosis

INTRODUCTION

Activation of the hemostatic system can occur in many clinical conditions. However, a systemic and strong activation of coagulation complicating clinical settings such as sepsis, trauma or malignant disease may result in the occurrence disseminated intravascular coagulation (DIC). Areas covered: This article reviews the clinical manifestation and relevance of DIC, the various conditions that may precipitate DIC and the pathogenetic pathways underlying the derangement of the hemostatic system, based on clinical and experimental studies. In addition, the (differential) diagnostic approach to DIC is discussed. Expert commentary: In recent years a lot of precise insights in the pathophysiology of DIC have been uncovered, leading to a better understanding of pathways leading to the hemostatic derangement and providing points of impact for better adjunctive treatment strategies. In addition, simple diagnostic algorithms have been developed and validated to establish a diagnosis of DIC in clinical practice.

Interleukin-6 Stimulates Coagulation, not Fibrinolysis, in Humans

The role of IL-6 as a mediator of haemostatic changes during severe inflammation is controversial. To assess the effect of IL-6 on haemostasis we conducted a controlled cross-over study in eight patients with metastatic renal cell cancer. In all subjects coagulation and fibrinolysis were monitored during and after a 4-h infusion of either 150 μg recombinant human (rh) IL-6, or during infusion of saline (control study). Mean maximum IL-6 concentrations were 1418.0 ± 755.8 pg/ml. Compared to the control study, rhIL-6 induced activation of coagulation as reflected by a 190 ± 55% increase in the plasma levels of thrombin-antithrombin III complexes (p <0.001) and by a 24 ± 11% increase in the plasma levels of in the prothrombin activation fragment F1 + 2 (p <0.001). In contrast, fibrinolysis was not affected. We conclude that in severe inflammation IL-6 may contribute to the activation of coagulation, whereas other factors mediate changes in fibrinolysis.

Fibrinolytic Response to lnterferon-a in Healthy Human Subjects

Interferons (IFNs) are used for a variety of disorders. It has been postulated that part of the effects of IFN may be mediated by IFN-induced modulation of endothelial cells. Since the principal activating and inhibiting factors of the fibrinolytic system are synthesized and stored in endothelial cells, we have studied the effects on fibrinolysis and coagulation of the administration of recombinant IFN-α (5 × 106U/m2) to healthy human subjects (n = 8) in a randomized controlled cross-over study. IFN-α significantly increased plasma levels of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). Simultaneously, plasma levels of the inhibitor of plasminogen activation, PAI-1, sharply increased. The net effect on plasma plasminogen activator activity (PA-activity) was a modest increase to 116% of baseline, however without a significant effect on plasmin generation, as reflected by plasma levels of plasmin-α2-antiplasmin complexes. IFN-α had no effect on the plasma levels of thrombin-antithrombin III (TAT) complexes.

We conclude that despite considerable effects on endothelial cells, IFN-α does not significantly alter the coagulant-fibrinolytic balance, although the occurrence of such changes under pathological circumstances is not excluded.

Complete Inhibition of Endotoxin-Induced Coagulation Activation in Chimpanzees with a Monoclonal Fab Fragment against Factor VII/VIIa

Gram-negative sepsis is oftentimes complicated by activation of coagulation with disseminated intravascular coagulation and microthrombosis. This may contribute to the associated morbidity, multiple organ failure and death. Recent studies have established that the tissue factor-dependent pathway of blood coagulation has a significant participatory role in the initial endotoxin-induced activation of coagulation. Tissue factor (TF), expressed on the surface of activated monocytes and endothelial cells forms cell surface complexes with free circulating factors VII and VIIa. The latter complex proteolytically activates factors X and IX. Recent in vivo experiments have shown that a rapidly neutralizing TF monoclonal antibody prevents and arrests the endotoxin- induced activation of coagulation and similar studies have shown to reduce mortality in baboons. In this study we describe the preparation of a factor VII/VIIa neutralizing monoclonal Fab fragment and characterize its effect on in vivo activation of coagulation during experimental endotoxemia in chimpanzees.

Four chimpanzees received a bolus intravenous injection of 4 ng/kg endotoxin in combination with Fab fragments of a factor VII/VIIa neutralizing murine monoclonal antibody (12D10) at a dose of either 50 μg/kg (n = 2) or 100 μfig/kg (n = 2). Four control animals received a bolus injection of endotoxin alone. Administration of the 12D10 Fab fragments, immediately preceding the endotoxin bolus injection, effectively blocked the endotoxin-induced activation of coagulation. Plasma levels of products of in vivo activation, namely F1+2, TAT complexes and FpA remained at baseline values. The administration of 12D10 resulted in a rapid decline in factor VII/VIIa antigen levels which remained below 5 ng/ml for 180-240 min, followed by a rapid return to baseline levels. Endotoxin administration resulted in activation of the fibrinolytic system as reflected by a rapid increase in plasma plasmin- α2-antiplasmin complexes. Administration of 12D10 was without effect on the endotoxin-induced fibrinolytic activation.

In conclusion, this study confirmed the importance of the TF: VII complex in the initial, endotoxin-induced activation of coagulation which was completely blocked by neutralizing all free and tissue factor-complexed factor VII/VIIa by a specific monoclonal Fab fragment. Activation of fibrinolysis was not influenced. Therefore, neutralization of factor VII/VIIa might be a promising therapeutic option in preventing endotoxin-induced microthrombosis during Gram-negative sepsis.

Assessment of the Relative Contribution of Different Protease Inhibitors to the Inhibition of Plasmin In Vivo

It has been shown that the most important inhibitor of plasmin is α2-antiplasmin, however, other protease inhibitors are able to inhibit this proteolytic enzyme as well. The contribution of the various protease inhibitors to the inhibition of plasmin in vivo has never been quantitatively assessed.

To assess the relative contribution of the different protease inhibitors on the inhibition of plasmin we developed a series of sensitive immunoassays for the detection of complexes between plasmin and the protease inhibitors α2-antiplasmin, α2-macroglobulin, antithrombin III, α1antitrypsin and C1-inhibitor, utilizing monoclonal antibodies that are specifically directed against complexed protease inhibitors and a monoclonal antibody against plasmin.

It was confirmed that α2-antiplasmin is the most important inhibitor of plasmin in vivo, however, complexes of plasmin with α2-macroglobulin, antithrombin III, α1antitrypsin- and C1-inhibitor were also detected. Particularly during activation of fibrinolysis complexes between plasmin and inhibitors other than α2-antiplasmin were detected. It was observed that during different situations the inhibition profile of plasmin was not constant e.g. in patients with diffuse intravascular coagulation plasma levels of plasmin-α1-antitrypsin and plasmin-C1-inhibitor were increased whereas in plasma from patients who were treated with thrombolytic agents complexes of plasmin with α2-macroglobulin and with antithrombin III were significantly elevated.

In conclusion, we confirmed the important role of α2-antiplasmin in the inhibition of plasmin, however, in situations in which fibrinolysis is activated other protease inhibitors also account for the inhibition of plasmin in vivo. Further investigations to assess the role of the various protease inhibitors in the fibrinolytic system can be assisted by the assays described in this study.

Deep Vein Thrombosis in Obstetric Patients: Diagnosis and Risk Factors

This study was performed to assess the prevalence of deep vein thrombosis (DVT) in consecutive obstetric patients with clinical symptoms of DVT, using impedance plethysmography (IPG) as the diagnostic method and to establish the safety of withholding anticoagulant therapy in patients with a repeatedly normal IPG. In addition, in patients with DVT the prevalence of coagulation and fibrinolytic disorders, which may explain the occurrence of venous thrombosis was investigated.Of the 77 obstetric patients with symptoms of DVT 32 (42%) had an abnormal IPG. The remaining 45 patients had a repeatedly normal IPG and showed no venous thromboembolism during a 6 months follow-up period. Twenty percent (six patients) of the patients with an abnormal IPG had a coagulation or fibrinolytic abnormality. These observations suggest that serial IPG can be used effectively in the management of obstetric patients with clinically suspected DVT and that hemostatic abnormalities are frequently found in those patients with DVT

Plasminogen Activation In Vivo upon Intravenous Infusion of DDAVP

Infusion of desamino-d-arginine vasopressin (DDAVP) results in an increase in plasma plasminogen activator activity. Whether this increase results in the generation of plasmin in vivo has never been established.

A novel sensitive radioimmunoassay (RIA) for the measurement of the complex between plasmin and its main inhibitor α2 antiplasmin (PAP complex) was developed using monoclonal antibodies preferentially reacting with complexed and inactivated α2-antiplasmin and monoclonal antibodies against plasmin. The assay was validated in healthy volunteers and in patients with an activated fibrinolytic system.

Infusion of DDAVP in a randomized placebo controlled crossover study resulted in all volunteers in a 6.6-fold increase in PAP complex, which was maximal between 15 and 30 min after the start of the infusion. Hereafter, plasma levels of PAP complex decreased with an apparent half-life of disappearance of about 120 min. Infusion of DDAVP did not induce generation of thrombin, as measured by plasma levels of prothrombin fragment F1+2 and thrombin-antithrombin III (TAT) complex.

We conclude that the increase in plasminogen activator activity upon the infusion of DDAVP results in the in vivo generation of plasmin, in the absence of coagulation activation. Studying the DDAVP induced increase in PAP complex of patients with thromboembolic disease and a defective plasminogen activator response upon DDAVP may provide more insight into the role of the fibrinolytic system in the pathogenesis of thrombosis.

DDAVP Induces Systemic Release of Urokinase-Type Plasminogen Activator

The desamino-d-arginine vasopressin (DDAVP) induced enhancement of endogenous fibrinolysis is generally attributed to the release of tissue-type plasminogen activator (t-PA) from the vessel wall.

The observation of concurrent release of urokinase-type plasminogen activator (u-PA), which eventually might cooperate in the enhanced fibrinolytic activity, has not been reported thusfar.

In a preliminary study in two healthy human volunteers we found a 1.8-fold increase of urokinase-antigen (UK-antigen) and a 1.7-fold increase of plasmin-activatable pro-urokinase (pro-UK) activity to DDAVP intravenously. The plasma-peak levels coincided with the maximal t-PA level. These responses following infusion of DDAVP were subsequently confirmed in a randomized double blind cross-over study in six human volunteers. We conclude that u-PA is released by DDAVP concurrently with t-PA and that it is presumably from the same origin as t-PA i.e. endothelial cells. u-PA and t-PA may therefore cooperate in the enhanced fibrinolytic activity upon DDAVP infusion.

Effects of Standard Heparin and a Low Molecular Weight Heparin (Kabi 2165) on Fibrinolysis

Previous and recent reports have suggested a fibrinolysisenhancing property of standard heparin and low molecular weight heparins, but these observations have never been confirmed in a study fulfilling appropriate methodological criteria. The aim of this study was to evaluate the effect of standard heparin and a low molecular weight heparin (Kabi 2165) on fibrinolysis in a randomized cross-over double blind placebo controlled study. Six healthy volunteers received intravenously a bolus dose of the following treatments: placebo; standard heparin, 5,000 I.U.; Kabi 2165, 5,000 anti-Xa U; Kabi 2165,10,000 anti-Xa U. Before the injection and at established times thereafter, blood samples were collected for the following assays in plasma: t-PA activity, PA inhibitor activity, fibrin plate lysis area (FPLA), plasminogen, α2-antiplasmin, fibrinogen and anti-Xa activity. Placebo and Kabi 2165, 5,000 anti-Xa U, had no effect on t-PA plasma level. Standard heparin and Kabi 2165, 10,000 anti-Xa U, produced a statistically significant increase in t-PA level at 1 hour after the infusion. This increase lasted for at least 1 hour after the infusion. No effect of any treatment on PA inhibitor, plasminogen, FLPA, α2-antiplasmin and fibrinogen was observed. We conclude that an intravenous bolus dose of both standard heparin, 5,000 I.U. and Kabi 2165, 10,000 anti-Xa U produces a delayed and sustained increase in plasma t-PA.

Hemostasis and Thrombosis in Extreme Temperatures (Hypo- and Hyperthermia)

The delicate biochemistry of coagulation and anticoagulation is greatly affected by deviations from the optimal temperature required for the interactions between various coagulation enzymes, cellular receptors, and intracellular mechanisms. Hyperthermia will lead to a prothrombotic state and, if sufficiently severe such as in heatstroke, a consumption coagulopathy, which will clinically manifest with the simultaneous appearance of intravascular thrombotic obstruction and an increased bleeding tendency. Hypothermia slows down the coagulation process, but as this seems to be adequately balanced by impairment of anticoagulant and fibrinolytic processes, its clinical effects are modest; however, hypothermia may be modestly linked to a somewhat higher risk of localized thrombosis. Restoration of a normal body temperature in patients affected by hyper- or hypothermia is the cornerstone for the management of associated coagulation derangements.

The role of ADAMTS-13 in the coagulopathy of sepsis

The interaction between platelets and the vessel wall is mediated by various receptors and adhesive proteins, of which von Willebrand factor (VWF) is the most prominent. The multimeric size of VWF is an important determinant of a more intense platelet-vessel wall interaction, and is regulated by the VWF-cleaving protease ADAMTS-13. A deficiency in ADAMTS-13 leads to higher concentrations of ultralarge VWF multimers and pathological platelet-vessel wall interactions, in its most typical and extreme form leading to thrombocytopenic thrombotic purpura, a thrombotic microangiopathy characterized by thrombocytopenia, non-immune hemolysis, and organ dysfunction. Thrombotic microangiopathy associated with low levels of ADAMTS-13 may be a component of the coagulopathy observed in patients with sepsis. Here, we review the potential role of ADAMTS-13 deficiency and ultralarge VWF multimers in sepsis, and their relationship with sepsis severity and prognosis. In addition, we discuss the possible benefit of restoring ADAMTS-13 levels or reducing the effect of ultralarge VWF as an adjunctive treatment in patients with sepsis.

Use of recombinant factor VIIa in the perioperative period

Recombinant activated factor VII (rFVIIa) is a pro-haemo -static agent that can be used for patients with haemophilia and inhibiting antibodies towards a coagulation factor. Recombinant factor VIIa is, however, increasingly used for several other indications, including patients who experience serious and life-threatening bleeding. In addition, rFVIIa has been evaluated for the prevention of major blood loss in patients undergoing surgical procedures that are known to be associated with major blood loss. In this manuscript we review the data on efficacy and safety of rFVIIa in the prevention of excessive blood loss and trans-fusion requirements in the perioperative period.

We conclude that recombinant factor VIIa is a promising agent for perioperative prevention of major blood loss but that its efficacy will probably vary between specific clinical settings. Its exact place in surgery warrants further clinical trials in various situations that will also more precisely determine the safety of this intervention.

The coagulant response in sepsis and inflammation

Critically ill patients often have systemic activation of both inflammation and coagulation. Increasing evidence points to an extensive cross-talk between these two systems, whereby inflammation not only leads to activation of coagulation, but coagulation also considerably affects inflammatory activity. The intricate relationship between inflammation and coagulation may have major consequences for the pathogenesis of microvascular failure and subsequent multiple organ failure, as a result of severe infection and the associated systemic inflammatory response. Molecular pathways that contribute to inflammation-induced activation of coagulation have been precisely identified. Activation of the coagulation system and ensuing thrombin generation is dependent on an inter-leukin-6-induced expression of tissue factor on activated mononuclear cells and endothelial cells and is insufficiently counteracted by tissue factor pathway inhibitor. Simultaneously, endothelial-bound anticoagulant mechanisms, in particular the protein C system and the antithrombin system, are shut-off by pro-inflammatory cytokines. Modulation of inflammatory activity by activation of coagulation also occurs by various mechanisms. Activated coagulation proteases, such as the tissue factor-factor VIIa complex, factor Xa and thrombin can bind to protease-activated receptors on various cells and the ensuing intracellular signaling leads to increased production of pro-inflammatory cytokines and chemo kines. Physiological anticoagulants can modulate inflammatory activity as well. Increasing knowledge on the various mechanisms underlying activation of inflammation and coagulation may lead to better (adjunctive) management strategies in critically ill patients.

Anticoagulants

Anticoagulants are effective in the prevention and treatment of a variety of arterial and venous thrombotic disorders but are associated with an increased risk of serious bleeding complications. Based on well documented studies of patients using vitamin K antagonists the incidence of major bleeding is 0.5%/year and the incidence of intracranial bleeding is 0.2%/year, however, in real life practice this incidence may be even higher. Risk factors for bleeding are the intensity of anticoagulation, the management strategy to keep the anticoagulant effect in the desired range, and patient characteristics. Recently, a new generation of anticoagulants have been developed and is currently evaluated in clinical trials. Initial results show a similar or superior efficacy over conventional anticoagulant agents with a good safety profile. In case of serious bleeding complications in a patient who uses vitamin K antagonists, this anticoagulant treatment can be quickly reversed by administration of vitamin K or coagulation factor concentrates. For the newer anticoagulants, quick reversal strategies are more cumbersome, although some interventions, including prothrombin complex concentrates, show promising results in initial experimental studies.

Bleeding risk assessment and management in atrial fibrillation patients

In this executive summary of a Consensus Document from the European Heart Rhythm Association, endorsed by the European Society of Cardiology Working Group on Thrombosis, we comprehensively review the published evidence and propose a consensus on bleeding risk assessments in atrial fibrillation (AF) patients. The main aim of the document was to summarise ‘best practice’ in dealing with bleeding risk in AF patients when approaching antithrombotic therapy, by addressing the epidemiology and size of the problem, and review established bleeding risk factors. We also summarise definitions of bleeding in the published literature. Patient values and preferences balancing the risk of bleeding against thromboembolism as well as the prognostic implications of bleeding are reviewed. We also provide an overview of published bleeding risk stratification and bleeding risk schema. Brief discussion of special situations (e.g. periablation, peri-devices such as implantable cardioverter defibrillators [ICD] or pacemakers, presentation with acute coronary syndromes and/or requiring percutanous coronary interventions/stents and bridging therapy) is made, as well as a discussion of the prevention of bleeds and managing bleeding complications. Finally, this document puts forwards consensus statements that may help to define evidence gaps and assist in everyday clinical practice.

Low-molecular Weight Heparins in Venous and Arterial Thrombotic Disease

Introduction: Since the introduction of low-molecular-weight heparins (LMWHs) in the early 1980's, the use of these compounds has been extensively investigated as a substitute for unfractionated heparin (UFH) in patients with venous and arterial thrombotic diseases. LMWHs have several advantages as compared to UFH, such as the subcutaneous route of administration, the predictable anticoagulant response and the lack of the need for laboratory monitoring. The present systematic review evaluates randomised clinical trials which investigated the efficacy and safety of LMWH in the acute treatment of venous thromboembolims, myocardial infarction, unstable coronary syndromes and ischemic stroke.

Methods: A computerised and manual search was performed to identify all relevant clinical trials. All randomised studies, with an a priori defined study population, clinical outcome measurement and adequate follow-up, were reviewed by two independent assessors. Whenever possible a common effect estimate of the included studies was calculated.

Results: Thirteen studies in approximately 4000 patients with acute venous thromboembolism revealed an odds ratio for the 3-month recurrent thromboembolism rate and major bleeding complications during exposure of 0.77 (C.I. 0.57-1.04) and 0.61 (C.I. 0.39-0.95), respectively, in favour of LMWH as compared to UFH. In patients with acute myocardial infarction, one study suggested a reduction in the incidence of reinfarction and cardiac death in LMWH recipients compared to UFH, while a placebo-controlled study revealed no beneficial effect of LMWH on these outcomes. In six studies including over 7000 patients with acute unstable coronary syndromes, there was an odds ratio for recurrent angina, myocardial infarction, urgent revascularisation and major bleedings of 0.88 (C.I. 0.76-1.01), 0.84 (C.I. 0.69-1.01), 0.83 (C.I. 0.70-0.99), 1.09 (C.I. 0.70-1.70), respectively, in favour of LMWH compared to UFH. The three studies comparing LMWH treatment with placebo in approximately 1000 patients with acute ischemic stroke revealed an odds ratio for the 10-day recurrent stroke, death or disability after 3 months and major bleeding complications of 0.68 (C.I. 0.41-1.13), 0.94 (C.I. 0.78-1.15), 2.92 (C.I. 1.88-4.55), respectively.

Conclusion: Fixed-dose subcutaneous LMWH appears to be a safe and effective alternative for dose-adjusted intravenous heparin in the treatment of patients with acute venous thrombotic disease as well as in patients with acute unstable coronary syndromes. The effectiveness of LMWH in patients with acute myocardial infarction remains unclear. There seems to be no beneficial effect of LMWH treatment as compared to placebo in patients with acute ischemic stroke, while the risk of major bleeding was clearly increased.

Platelets Release Thrombopoietin (Tpo) upon Activation: another Regulatory Loop in Thrombocytopoiesis?

Thrombopoietin is produced at a constant rate by the liver and kidney and is removed from the circulation upon binding and subsequent uptake via the Tpo receptor, c-Mpl, expressed by platelets and megakaryocytes. Apart from uptake, this study shows that platelets can also function as a storage pool for Tpo.

Upon stimulation with various platelet agonists, full-length biologically active Tpo was released by platelets. Platelet fractionation experiments indicated that this Tpo most likely is contained in the granules. When platelets were preincubated with Tpo-peptide mimetic or truncated Tpo prior to maximal activation, a three- to fivefold increment in Tpo release was seen, whereas, the release of other granule proteins such as vWF-propeptide or serotonin remained unchanged. Therefore, the Mpl agonists might compete with Mpl-bound Tpo, thereby releasing Tpo into the platelet supernatant.

Intravascular release of Tpo by platelets might occur in patients with massive platelet activation, as occurs in patients with disseminated intravascular coagulation. The Tpo concentration in these patients is elevated (p <0.01) and correlates with markers for thrombin generation, TAT complexes and Fl+2 (rp =0.8 and 0.9; p <0.01). This suggests that the increment in Tpo concentration was attributed to Tpo release by activated platelets in vivo, which might be instrumental in subsequent stimulation of thrombocytopoiesis.