2 Normal HemostasisFirst, injury to a blood vessel leads to immediate vasoconstriction, as well as activating the coagulation cascade.Platelet adhesion: results from exposure of blood to subendothelial collagenAdhesive proteins (von Willebrand factor and fibrinogen) mediate the adhesion of platelets to the subendotheliumPrimary hemostatic plug is formed after platelets aggregate.Platelet plug is unstable and short-lived, but serves as a framework for secondary hemostasis.
3 Normal HemostasisActivation of intrinsic pathway (contact phase) results in fibrin formationThis process occurs almost simultaneously with platelet adhesion and aggregation
4 Intrinsic PathwayFactor XII is activated by contact with subendothelial collagen and the platelet plugPrekallikrein and high molecular weight kininogen are important cofactors for factor XII activationFibrin (secondary hemostatic plug) is the result (through the Common Pathway)The secondary hemostatic plug is stable and long-lasting.
5 Extrinsic PathwayTissue factor (factor III) is released whenever there is tissue trauma, and this activates the extrinsic pathwayEnd result is also fibrin formation through the Common Pathway
8 Fibrinolysis Fibrinolysis prevents excessive thrombus (clot) formation It is activated by stimuli that activate the Intrinsic pathway (exposure to subendothelial collagen and the platelet plug)Plasminogen is activated and becomes Plasmin, which is responsible for lysis of a clot; as well as inhibition of platelet aggregation and activation of clotting factors in the affected area
9 Natural anticoagulants Other natural anticoagulants are activated by initiation of coagulation cascade (Antithrombin and proteins C and S).Antithrombin is a protein synthesized by hepatocytes, and inhibits the activation of factors IX, X, and thrombinActs as a cofactor for heparinProteins C and S are also produced by hepatocytes, and are Vitamin K-dependent
10 Important questions to ask owners when animal presents with spontaneous or excessive bleeding: Is this the first bleeding episode?Has the pet had any surgeries before this, and if so, did the pet bleed excessively?Do any littermates have similar clinical signs? Was there increased perinatal mortality in the litter?Has the pet recently been vaccinated (especially with modified-live vaccines)?Is the pet receiving any medications?Does the pet have access to rodenticides or does it roam freely?
11 Clinical signs association with disorder of primary hemostasis Petechiae, ecchymoses common on mucous membranes and skinBleeding from mucosal surfaces (epistaxis, gingival bleeding, hematuria, melena, hematochezia, hyphema)Prolonged bleeding after venipuncture
12 Clinical Signs associated with disorder of secondary hemostasis Hematomas are commonBleeding into muscles, joints, and body cavities (i.e. hemoabdomen, hemothorax)Delayed bleeding after venipunture
13 Coagulation tests Evaluation of blood smear Platelet numberPlatelet morphologyLook for platelet clumps and estimate platelet numberGeneral rule: # platelets/oil x 15,000 = estimated platelet count (plts/ul)Schizocytes (fragmented rbcs) suggest microangiopathic hemolysis (DIC)
14 Coagulation TestsBuccal mucosa bleeding time (BMBT): time in minutes for bleeding to cease from a standardized incision (laceration in upper lip)Evaluates formation of platelet plug and depends upon:Adequate number of plateletsAdequate function of plateletsNormal blood vessel wall structure
15 Coagulation TestsActivated partial thromboplastin time (APTT): time in seconds for clot formation in citrated plasma after addition of contact activator, phospholipid, and calciumPlatelets have no effect on this test since phospholipid is addedEvaluates intrinsic and common pathwaysDetects 30% or less factor activity in these pathways
16 Coagulation testsOne-stage prothrombin test (OSPT or PT): time in seconds for clot formation in citrated plasma after addition or thromboplastin and calciumPlatelets have no effect on test since adding tissue thromboplastin (factor III)Factor VII has the shortest half-lifeEvaluates Extrinsic and Common PathwaysDetects 30% or less factor activity
17 Coagulation testsThrombin clotting time (TCT): time in seconds for clot formation in citrated plasma after addition of thrombin and calciumMost sensitive measure of fibrinogen concentrationProlonged TCT with:Hypofibrinogenemia (DIC)Increased FDPs, D-dimersHeparin treatmentUremia
18 Coagulation testsFibrin degradation products (FDPs): formed when plasmin dissolves the fibrin clotUltimately are removed by the liver (half-life 9-12 hours).
19 Coagulation testsD-dimers: unique FDPs that are formed when cross-linked fibrin is lysed by plasminSpecific for active coagulation and fibrinolysisD-dimer is a sensitive test for DIC and likely is superior to traditional FDP assays for this purpose
20 Disorders of Primary Hemostasis In theory, spontaneous bleeding as a result of primary hemostatic defect could be due to one of three mechanismsThrombocytopenia (decrease platelet number)Thrombopathia (platelet dysfunction)Vascular defectThrombocytopenia is most common cause; others are rare.
22 Decreased platelet production Most common cause for thrombocytopenia in catsUsually caused by retrovirus-induced bone marrow disorders (FeLV)Other causes: Drugs (estrogen, phenybutazone, some chemo agents); toxins; radiation; infectious (FIV); neoplastic process in bone marrow; specific platelet infectious agents (Ehrlichia platys); pure megakaryocytic hypoplasia (rare)Diagnosis by bone marrow aspiration or biopsy
23 Increased platelet destruction Most common cause of thrombocytopenia in dogs; extremely rare in catsImmune-mediated:Primary: Idiopathic, Evan syndrome, systemic lupus erythematosusSecondary: Drugs, live-virus or modified-live virus vaccination, tick-borne disease, neoplasia, bacterial infection
24 Increased platelet consumption Occurs most commonly in dogs and cats with DICOther causes: Acute Hemorrhage, Neoplasia, Microangiopathies, Sepsis, vasculitis, splenic torsion, hyperslenism, hepatic disease, hemolytic uremia syndrome
26 Platelet dysfunctionCan be congenital (von Willebrand’s disease) or acquired – more commonRarely result in spontaneous bleedingAcquired causes - secondary to:Drug therapy (esp. aspirin, cephalosporins, B-lactams, synthetic colloids)UremiaNeoplasiaDICMonoclonal gammopathies (multiple myeloma, plasma cell )EhrlichiosisRetroviral infectionsSnake venom
27 Von Willebrand’s disease More common in dogs; rare in catsCommon in Doberman pinschers, GSD, Poodles, Golden retrievers, Shetland sheepdogs.vWF is produced by megakaryocytes and endothelial cells, and it circulates in plasma complexed to factor VIIIIt is important in the formation of the primary platelet plug (causes platelets to adhere to subendothelial cartilage)
28 vWD Usually see excessive bleeding during or after surgery Excessive bleeding during teething and estrus can occurPerinatal mortality or abortion/stillbirths are common in litters with vWDBMBT is most cost effective screening test in at-risk breedsCan also send out blood to quantify vWF:<50% indicate vWF deficiency
29 Treatment of vWDFresh frozen plasma, whole fresh blood, or cryoprecipitate - causes the circulating vWF concentration to increase within minutesDesmopressin acetate – causes massive release of vWF from endothelial cellsCan use topical hemostatic agents (fibrin, collagen, methacrylate) to control local bleeding
30 Disorders of secondary hemostasis: Congenital Specific factor deficienciesClinical severity depends on magnitude of factor deficiency and the exposure of the animal to trauma that may cause bleeding.Most animals develop bleeding in the first year of life.Mildly affected animals may not bleed until later in life, especially if they do not undergo surgery or trauma.
31 Inherited Coagulopathies Should be suspected in younger animals, esp taking breed into accountShould be suspected if there is a history of recurrent bleedingIf acquired causes have been ruled outDiagnosis requires specific factor assays performed by specialized laboratories.
32 Inherited Coagulopathies Treatment is aimed at controlling bleedingIf bleeding is severe, transfusion of plasma products is indicated to provide needed clotting factor(s).For deficiencies of factors VIII and I, cryoprecipitate is the ideal plasma product.For deficiencies of factors II, VII, IX, X, and XI, cryosupernatant is ideal.Fresh frozen plasma is an acceptable alternative.
33 Disorders of Secondary Hemostasis: Acquired Vitamin K deficiency and antagonismHepatic diseaseDIC
34 Vitamin K deficiencySynthesis of Vitamin K-dependent factors occurs in the liverFactors II, VII, IX, XVitamin K is an essential cofactor (for carboxylation) to activate these factorsAnticoagulant rodenticides interfere with recycling of Vitamin K, resulting in rapid depletionProteins C and S are also vitamin K-dependent
35 DiagnosisFactor VII has shortest half-life (4-6 hours), so will see prolongation in PT firstClinical signs usually occur 2-3 days after ingestionBy the time hemorrhage is seen, PT and APTT will be prolongedFDP, D-dimer, and fibrinogen concentrations are usually normalPlatelet count is usually normal, but can be decreased due to consumption
36 TreatmentFresh frozen plasma or whole fresh blood to replenish clotting factorsPrbc transfusion if animal is anemicVitamin K1 – 5mg/kg SC in multiple sites, followed by oral Vitamin K1 2.5mg/kg BID 12 hrs later (give with fatty meal to enhance absorption)May take 12 hours to shorten PT
37 Hepatic DiseaseSevere damage to hepatocytes or obstruction of bile duct results in variable factor deficiencies and/or abnormalities in Vitamin K metabolismDisorders of platelet number and function may occurPT and PTT can be prolongedFDP, D-dimer, and fibrinogen concentrations may be increased due to reduced clearance of plasminogen activators, as well as reduced synthesis of fibrinolytic inhibitors
38 Hepatic DiseaseBased on results of coagulation tests, may be difficult to differentiate from DICLook to physical exam findings, chemistry profile changes, and liver function testing.Treatment with fresh frozen plasma transfusion +/- Vitamin K1Repeat coags in 12 hrs to assess if Vitamin K1 was beneficial
39 Disseminated Intravascular Coagulation Excessive intravascular coagulation leads to multiple organ microthrombosis. Multiple organ failure (MOF) or multiple organ dysfunction syndrome (MODS) can be a consequence.Paradoxical bleeding occurs due to the inactivation or excessive consumption of platelets and clotting factors secondary to enhanced fibrinolysis.DIC is a complex syndrome, and is a common pathway in a variety of disorders
40 DICGeneral mechanisms leading to activation of intravascular coagulation:Endothelial damagePlatelet activationRelease of tissue procoagulants
41 DIC PathogenesisFirst, primary and secondary hemostatic plugs form in multiple small vessels simultaneously, forming multiple thrombi in the microcirculationIschemia is the result, leading to MOF or MODSPlatelets are consumed in large numbers, leading to thrombocytopenia
42 DIC PathogenesisSecond, fibrinolytic system is activated, and this results in clot lysis and the inactivation of clotting factors and impaired platelet function.Third, antithrombin and possibly proteins C and S are consumed in an effort to stop intravascular coagulation. This effectively depletes these anticoagulants.Fourth, fibrin formation in the microvasculature causes shearing of rbc’s (schistocytes), and leads to hemolytic anemia.
43 DICExcessive intravascular coagulation and depletion of natural anticoagulants leads to spontaneous bleeding as a result of:ThrombocytopeniaImpaired platelet functionInactivation of clotting factors
45 DIC: Clinical signs Chronic, clinically silent form Acute, fulminant formNo spontaneous bleedingAbnormalities seen on blood work points to DICCommon with malignancy and possibly other chronic disordersPresent for evaluation of primary problemAfter heat stroke, electrocution, acute pancreatitisOr, acute decompensation of chronic, silent form (i.e. HSA)Profuse, spontaneous bleeding, plus signs secondary to anemia and MOFBoth primary and secondary bleedingExtremely rare in cats
46 Diagnosis Hemostatic abnormalities CBC/Chem/UA Thrombocytopenia, prolonged PT and APTT, normal or low fibrinogen concentration, positive FDP and/or D-dimer test, decreased antithrombin concentrationRegenerative hemolytic anemia, or nonregenerative anemiaHemoglobinemia, SchnistocytesThrombocytopenia, neutrophilia with left shift, or rarely neutropeniaHyperbilirubinemia, azotemia and hyperphosphatemia, increased liver enzymes, decreased TCO2, panhypoproteinemiaHemoglobinuria and bilirubinuria
47 Treatment Stopping intravascular coagulation Maintaining good organ perfusionPreventing secondary complicationsGrave prognosisNegative prognostic indicators are marked prolongation of APTT and severe thrombocytopeniaPrognosis depends on how many abnormalities are identified on coagulation tests
48 Thrombosis/Thromboembolism CausesStasis of bloodActivation of IV coagulation in an area of damaged or abnormal endotheliumDecreased activity of natural anticoagulantsDecreased or impaired fibrinolysis
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