1. The Clotting Cascade and DIC
Karim Rafaat, MD

2. Coagulation
Coagulation is a host defense system that maintains the integrity of the high pressure closed circulatory system
To prevent excessive blood loss after injury the hemostatic system
Endothelial cells
Platelets
Plasma coagulation proteins

3. Coagulation Immediately after injury, primary hemostasis occurs
Vascular constriction
Platelet activation
Primary hemostasis-
Vascular constriction
Platelet activation
Adhesion- collagen in vascular endothelium exposed; vWF binds to exposed endothelial matrix and also binds platelets by glycoprotein receptor (Ib/V) on platelet surface
Aggregation- after adhesion, glycoprotein IIB/IIIa receptor on platelet surface is activated by inducing a conformational change. This receptor binds fibrinogen and fibrinogen links adjacent platelets resulting in aggregation
After adhesion/aggregation, platelet granules synthesize and release ADP, platelet activating factor, and serotonin which stimulate and recruit more platelets; thromboxane A2 (TXA) is a potent vasoconstrictor; platelet derived growth factor stimulates smooth muscle regrowth/repair

5. Coagulation Secondary hemostasis
Stabilizes an otherwise unstable platelet plug by adding fibrin to the clot

7. Vascular Surface Changes
Intrinsic Pathway
Vascular Surface Changes
Kallikrein +HMWK
HMWK T
Ca+
VIII
VIIIa
VIIIa/IXa
Intrinsic Path- Pathway happens by substances already found IN the vascular space; Prekallikrein, high-molecular weight kininogen, factor 12 circulating in plasma exposed to negatively charged ions on collagen initiate pathway
Factor 12, known as Hageman; Hageman who found it died of a PE
Factor 9a binds to factor 8a on the surface of activated platelets; hemophilia B
Factor 8 circulates in the plasma bound to vWF; cleaved free by thrombin; hemophilia A
8A/9A complex called tenase
Calcium required as co-factor along way, so calcium binders like citrate are anticoagulants
Intrinsic path overall plays small roll in actual clotting after injury as patients with factor 12, prekallikrein, high-molecular weight kininogen deficiencies will not have bleeding tendencies (but will have markedly elevated PTT)

8. Tissue Factor Extrinsic Pathway VIIa/TF
Extrinsic Path- Pathway happens by substances found OUTSIDE the vascular space; Tissue factor is a non-enzymatic lipoprotein on the surface of cells not normally in contact with plasma..i.e. fibroblasts and macrophages; tissue factor is also expressed by endothelial cells when endotoxin, TNF, IL-1 present in circulation; when tissue factor comes in contact with plasma, it binds circulating factor 7 and activates this proenzyme to it’s active form factor 7A; factor 7A causes 30,000 fold increase in rate of factor X activation
Factor Xa can increase VIIa production/binding to TF

9. Common Pathway Xa/Va Va V
Common Pathway- Factor 13 produces strong disulfide bonds in fibrin polymer
Ca+ T
Ca+
Ca+
Xa/Va Va V

10. Fibrinolytic System Dissolves the occlusive fibrin clot
Restores vessel patency
Allows normal healing of vessel

11. Plasmin X Plasminogen TPA/Uro
Plasminogen is inactive protein cleaved to plasmin by tissue plasminogen activator (TPA) and urokinase; TPA/urokinase are products of endothelial cells; fibrin breaks down and leaves fibrin split products/D-dimer
Fibrin Split Products
+ D-Dimer X

12. Anticoagulants Several natural anticoagulants exist
Prevents “over” coagulation
Deficiencies result in prothrombotic states

13. X Antithrombin III X Activated Protein C X X Protein C X Tissue Factor
Pathway Inhibitor X
Antithrombin III X
Activated Protein C
Endothelial receptor binds thrombin; when bound, conformation change results in thrombomodulin, which activates Protein C along with co-enzyme protein S; activated protein C degrades cofactors 8A and 5a
Antithrombin III- serine protease inhibitor that binds and degrades Xa/Thrombin/X1/1X; always present, but adhesion increases in heparin use
Tissue Factor Pathway Inhibitor- proten mediates feedback inhibition of TF/VIIa complex
Protein S X X
Protein C
Thrombomodulin X

14. Laboratory Evaluation of Coagulation
aPTT
Pt plasma incubated with surface-active powder (silica)
Measures intrinsic pathway and common pathway
aPTT= activated partial thromboplastin time; measures intrinsic pathway; Nl PTT, intrinsic pathway ok and common pathway likely ok (although some exceptions); isolated prolongation of aPTT is caused by deficiencies of kallikrein, high molecular weight kininogen, factors 12, 11, 9, 8, by circulating anticoagulants (like lupus anticoagulant, factor 8 anticoagulant), and some disease processes like liver disease, DIC

15. Laboratory Evaluation of Coagulation
Evaluate abnormal PTT with 1:1 mixing study
Mixing study to evaluate elevated PTT; only 30-50% of nl coagulation factor level required for normal PTT; so mix patient plasma with normal plasma in 1:1 mix (giving at least 50% of correct factors); if corrects, then prolongation is factor deficiency, if not, then patient plasma contains coagulation inhibitor

16. Laboratory Evaluation of CoagulationPT
Pt plasma incubated with source of tissue factor
Extrinsic Pathway and Common Pathway
PT= prothrombin time; measures extrinsic pathway; NL PT, extrinsic pathway and common pathway working ok; isolated elevation of PT can indicate isolated factor 7 deficiency, presence of oral anticoagulants, and occasionally disease states like liver disease and DIC; however, PT more sensitive than PTT to detect deficiencies of common pathway (factor X, thrombin, fibrinogen) so mild deficiencies may have isolated elevation of PT
INR is ratio of patient’s PT to the lab control PT; standardizes for different strengths of reagents used to start reaction

17. Laboratory Evaluation of Coagulation
Both PT/PTT elevated, typically common pathway deficiency or
disease state like
liver dsx/DIC

18. Disseminated Intravascular Coagulation
Consumption coagulopathy, Defibrination syndrome
Systemic activation of coagulation
Intravascular deposition of fibrin
Microvascular occlusion/thrombosis and organ ischemia
Thromboembolic disease
Consumption of coagulation factors and platelets
Bleeding if exhausted
Particularly in the microvasculature

19. Disseminated Intravascular Coagulation
Pathophysiology
Tissue factor activitation and coagulation
Impaired fibrinolysis
Defective anticoagulation pathways

20. Pathophysiology of DIC
Impaired fibrinolysis by elevated levels of plasminogen activator inhibitor type 1
Defective anticoagulation by decreased antithrombin III, protein C

21. Tissue Factor Activation
Extrinsic pathway exclusive as etiology of fibrin deposition in DIC
Activated by multiple pathologic states
Infection/sepsis
Trauma/head trauma
Malignancy
Vascular abnormalities
Obstetric complications
Tissue factor activation resulting in extrinsic pathway activation- DIC is EXCLUSIVELY mediated by extrinsic- multiple studies with no evidence for activation of other pathway; inhibition of extrinsic pathway in multiple experimental models of sepsis showed complete cessation of fibrin generation whereas blocking alternative pathways did not
Infection- gram negative endotoxin causes generation of tissue factor activity on plasma membrane of monocytes/endothelial cells; virus/parasites/exotoxins from gram + can cause DIC by generalized inflammatory response/systemic cytokines
Acute promyelocytic leukemia- hypergranular leukemic cells release material from their granules that has TF activity
Trauma-release of tissue material like fats into circulation as well as cytokines; Head trauma- break down of blood brain barrier, exposes blood to brain tissue with potent tissue factor activity
Vascular like Kasabach-Merritt/vascular aneurysms- local consumption
Obstetric- placenta abruption, retained fetus, amniotic fluid embolism

22. Impaired Fibrinolysis
Bacteremia results in rapid increase in fibrinolytic activity due to endothelial cell release of plasminogen activators
Rapid decline in fibrinolytic activity due to sustained increase of plasminogen activator inhibitor, type 1
Plasminogen
PAI-1
TPA/Urokinase
PAI-1 secreted by endothelium
PAI-1 knockout mice were challenged with endotoxin and there was complete lack of thrombi in kidneys compared to controls
Several clinical studies show high plasma PAI-1 levels is one of the strongest predictors in mortality
Plasmin X
Fibrin degredation
products/D-Dimer

23. Defective Anticoagulation Pathways
Tissue Factor
Pathway Inhibitor X
Antithrombin III X
Activated Protein C
Endothelial receptor binds thrombin; when bound, conformation change results in thrombomodulin, which activates Protein C along with co-enzyme protein S; activated protein C degrades cofactors 8A and 5a
Antithrombin III- serine protease inhibitor that binds and degrades Xa/Thrombin/X1/1X; always present, but adhesion increases in heparin use
Tissue Factor Pathway Inhibitor- proten mediates feedback inhibition of TF/VIIa complex
Protein S X X
Protein C
Thrombomodulin X

24. Defective Anticoagulation Pathways
Low levels of inactive protein C created due to downregulation of thrombomodulin by TNFalpha; low levels of free protein S for cofactor because it is bound to C4b binding protein, of which levels are very high in acute phase; low levels of protein C due to enhanced consumption, vascular leakage; sublethal dose of e coli into baboons that were then given C4BP resulted in severe DIC, organ damage, death
Antithrombin levels low because it is continuously consumed by ongoing clot formation, it is degraded by elastase that neutrophils make, and it leaks extravascularly in capillary leak syndrome; several clinical studies with average levels of 30% in patients with sepsis; restoration of antithrombin levels in experimental DIC in animals improves outcomes with less organ failure/mortality
Smaller contributor is decreased TFPI levels

25. Clinical Manifestations
No clinical manifestations with just abnormal labs to suggest diagnosis
Bleeding %
Thromboembolic %
Bleeding- cutaneous, GI, GU, pulmonary, surgical sites
Thromboembolic-aggrevated multiorgan dysfunction, i.e. kidney failure worse, etc

26. Diagnosis
International Society on Thrombosis and Hemostasis, subcommittee on DIC
Sensitivity of predicting DIC 93%, specificity 98%; also very well correlated with 28 day mortality score
D-dimers proteolytic byproducts of plasmin degredation of x-linked fibrin polymers; can be elevated if recent surgery/trauma/etc (recent events)
Fibrin monomers tested by PPP- plasma protamine paracoagulation (ongoing fibrin formation)

27. Treatment Treat the underlying disease process!!!!
Replace platelets, FFP, cryoprecipitate, Vitamin K
Replace- Only replace if bleeding, doing a procedure, high risk for bleeding- platelets >10-20, Fibrinogen >100, close to normal coags; no e/o “adding fuel to fire”; one exception is head trauma patients- prone to rapid significant dec in low fibrin, low factor levels, low platelets that will return to normal within hours- however, because of their high risk of CNS bleed, fix the stuff until it fixes itself!

28. Treatment
Heparin
Subacute/chronic DIC as in malignancy as more likely to have thromboembolic phenomenon
Acute DIC less commonly; consider if intensive replacement therapy doesn’t alleviate bleeding/correct coags
80u/kg bolus then 18u/kg/hr
Pathophys- Tissue factor activitation and coagulation, Impaired fibrinolysis, Defective anticoagulation pathways
Or any other patient that has thromboembolic predominating disease- ie. In acute DIC, consider in purpura fulminans as thrombus formation predominates

29. Treatment Recombinant tissue pathway factor inhibitor
Inhibits VIIa/TF binding to factor X
OPTIMIST trial
96 hr continuous infusion of rTPFI vs placebo
Efficacy end point 28 day mortality
Additional analysis of organ dysfunction, biomarkers of inflammation and coagulation
Pathophys- prevents initiation of extrinsic pathway
OPTIMIST- large phase 3, randomized placebo-controlled trial, 1754 patients; patients with SIRS, evidence of organ dysfunction, INR >1.2
Levels low in DIC, but smaller percentage of contribution than decreased protein C/S or antithrombin III

30. Treatment Recombinant tissue pathway factor inhibitor OPTIMIST trial
rTPFI mortality 34.2%, placebo mortality 33.9%
Trend toward mortality benefit in pts with documented bloodstream infections or documented PNA
Mortality no significant difference; p .75
Interestingly, first half of trial results with overwhelming improvement in mortality and vice versa at end of trial, ? why

31. Treatment Antithrombin III
Inhibits multiple clotting factors; most potently thrombin
First transfused in pts with DIC in 1978 by Schipper
Multiple animal studies with improved lab parameters, shortened duration of DIC, improved organ fxn, AND improved mortality
Animal studies with all sorts of infection- gram neg, gram pos, polymicrobial)

32. Treatment Antithrombin III Fourrier et al, 1993 Inthorn et al, 1997
35 pts septic shock, DIC
44% relative risk reduction in sepsis mortality
Inthorn et al, 1997
45 pts septic shock, DIC; co-adm with heparin gtt
14% relative risk reduction in mortality
Schuster et al, 1998
42 pts septic shock, DIC
39% relative risk reduction in mortality
Inthorn- suggestion of excess bleeding in coadministration groups
Meta-analysis of these three estimated a 22.9% reduction in 30 day all cause mortality with use of ATIII

33. Treatment Antithrombin III Large phase III multinational sepsis study
2314 patients worldwide
No improvement in 28 day mortality compared to placebo
Study population not as sick as they had hoped to enroll
Failure to achieve target blood level of ATIII
SIGNIFICANT bleeding risk if co-administer of even low dose heparin
Initial target population was pts with predicted mortality by SAPS score of 30-60%; less than half study population met this criteria
Target blood level >200% normal but mean was only 180%; need supraphysiologic doses to work; there was significantly improved outcome in subsets of patients with AT levels >200% compared to those with % less