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HEMOSTASIS HEMOSTASIS COMPONENTS Vessel wallVessel wall PlateletsPlatelets Coagulation enzymesCoagulation enzymes Fibrinolytic systemFibrinolytic system.

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Presentation on theme: "HEMOSTASIS HEMOSTASIS COMPONENTS Vessel wallVessel wall PlateletsPlatelets Coagulation enzymesCoagulation enzymes Fibrinolytic systemFibrinolytic system."— Presentation transcript:

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2 HEMOSTASIS

3 HEMOSTASIS COMPONENTS Vessel wallVessel wall PlateletsPlatelets Coagulation enzymesCoagulation enzymes Fibrinolytic systemFibrinolytic system Control mechanisms, including inhibitorsControl mechanisms, including inhibitors NOTE: Normal hemostasis involves the complex interaction of the vessel wall, circulating proteins and biochemical mediators, cells, promoters and inhibitors. Activation of hemostasis usually begins with damage to the vessel wall, exposing the subendothelium. Conversely, the intact vessel wall helps to maintain fluidity of blood, not simply through being a passive container wall, but also by synthesizing chemicals and proteins that actively contribute to the process. When the vessel wall is damaged, platelets are at the forefront of defense by sticking to the damaged area. The clotting enzymes contribute by developing a fibrin mesh that holds the platelets in place. Control mechanisms come into play to limit hemostatic process to the are of injury. Otherwise the whole body would clot up at the slightest stimulus.

4 Sequence of Changes With Vascular Injury Injury to vessel wall (endothelium) with resultant exposure of subendotheliumInjury to vessel wall (endothelium) with resultant exposure of subendothelium Platelet adhesion mediated by HMW vWFPlatelet adhesion mediated by HMW vWF Simultaneous activation of clotting enzymesSimultaneous activation of clotting enzymes Platelet aggregation via fibrinogen receptors on plateletsPlatelet aggregation via fibrinogen receptors on platelets Anchoring of platelet plug by cross-linked fibrinAnchoring of platelet plug by cross-linked fibrin NOTE: Lets expand on the sequence of events that occur when a vessel wall is injured and define a few basic terms. Injury exposes the subendothelial collagen and the soluble substances that are normally between the subendothelium and collagen.

5 Normal Hemostasis Vessel Wall Exposed collagen Contraction vFW large multimers Tissue TPL Plateletadhesion Activation of Coagulation PlateletAggregation Thrombin 1º Hemostatic Plug DefinitiveHemostaticPlug Limiting Reactions This slide gives a diagrammatic representation of the whole process and the functional interrelationships. We will now go on to dissect the various components of this process in more detail.

6 Platelet Components RECEPTORS vWF Fibrinogen Clotting Factors Alpha granules Dense Granules Actin Canaliculus

7 Platelet Granules Alpha granulesAlpha granules –vWF –Fibrinogen –PF4 –Beta thromboglobulin –PDGF Dense granules (delta)Dense granules (delta) –ADP –Serotonin

8 Platelet Role in Hemostasis vFW binding sites- platelet adhesionvFW binding sites- platelet adhesion Fibrinogen binding sites- platelet aggregationFibrinogen binding sites- platelet aggregation Multiple binding sites for coagulationMultiple binding sites for coagulation factors - enhances appropriate steric relationships Production of multiple chemical mediators Production of multiple chemical mediators Binding sites for chemical mediators Binding sites for chemical mediators First, lets look more closely at the role of platelets. They play multiple roles in the hemostatic process, and, contrary to the view held 30 years ago, when they were thought to a small part of the process, many would now consider them to have a central role. We already have alluded to this by indicating that the first step after injury is platelet adhesion to the subendothelium. This is mediated by subendothelial HMW vWF binding to specific receptor sites on the platelet membrane. In, addition there binding sites that play a role in virtually every step of the process. Also. chemical mediators are synthesized by internal organelles, and they contain a contractile protein that is responsible for clot retraction. The coagulation enzymes are present in relative low concentrations in plasma. Binding of certain of these factors to specific receptors on the surface of activated platelets allows them to line up in appropriate steric configuration, catalyzing the process and limiting the reactions to the area of injury.

9 von Willebrands Factor Synthesized in megakaryocytes and endothelial cells - approx. 230,000 M.W.Synthesized in megakaryocytes and endothelial cells - approx. 230,000 M.W. Macromolecular multimer plasma: M.W. 1 x X10 6. Plasma carrier of Factor VIII, stabilizes itMacromolecular multimer plasma: M.W. 1 x X10 6. Plasma carrier of Factor VIII, stabilizes it Large molecular forms:Large molecular forms: a. Most effective in platelet adhesion b. Predominate in endothelial cells and subendothelium

10 Coagulation Cascade TISSUE FACTOR FACTOR VII VIIa (ACTIVATED) ( XI?) IX IXa TFPI VIII FACTOR X Xa V, Ca FACTOR II IIa FIBRINOGEN FIBRIN MONOMERS FACTOR XIII IN VITRO CROSS-LINKED FIBRIN PT (STABLE FIBRIN CLOT) APTT CONTACT ACTIVATION FXII, FXI, FLETCHER, FITZGERALD FACTORS VIII IX IXa PT PHOSPHOLIPID PLATELET ACTIVATION INHIBITION OF CLOTTING THROMBOMODULIN PROTEIN C

11 Coagulation Cascade- PT TISSUE FACTOR FACTOR VII VIIa (ACTIVATED) ( XI?) IX IXa TFPI VIII FACTOR X Xa V, Ca FACTOR II IIa FIBRINOGEN FIBRIN MONOMERS FACTOR XIII IN VITRO CROSS-LINKED FIBRIN PT (STABLE FIBRIN CLOT) APTT CONTACT ACTIVATOR FXII, FXI, FLETCHER, FITZGERALD FACTORS VIII IX IXa PT PHOSPHOLIPID PLATELET ACTIVATION INHIBITION OF CLOTTING THROMBOMODULIN PROTEIN C (ENDPOINT) PHOSPHOLIPID

12 Coagulation Cascade- APTT TISSUE FACTOR FACTOR VII VIIa (ACTIVATED) ( XI?) IX IXa TFPI VIII FACTOR X Xa V, Ca FACTOR II IIa FIBRINOGEN FIBRIN MONOMERS FACTOR XIII IN VITRO CROSS-LINKED FIBRIN PT (STABLE FIBRIN CLOT) APTT CONTACT ACTIVATOR FXII, FXI, FLETCHER, FITZGERALD FACTORS VIII IX IXa PT PHOSPHOLIPID PLATELET ACTIVATION INHIBITION OF CLOTTING THROMBOMODULIN PROTEIN C (ENDPOINT)

13 Control Mechanisms Intact endothelial cellsIntact endothelial cells –Chemical mediators –Membrane bound receptors –Synthesizes activators of fibrinolysis Circulating inhibitorsCirculating inhibitors –Protein C system Fibrinolytic systemFibrinolytic system –Endothelial component –plasma protein component

14 NOPGI 2 ADPase INHIBITS PLATELET ACTIVATION THROMBOMODULIN PROTEIN C PROTEIN Ca PROTEIN S INACTIVATES Va + VIIIa ATIII INHIBITS Xa + THROMBIN PLASMINOGEN ACTIVATORS (tPA) (uPA) PLASMINOGEN PLASMIN FIBRINOLYSIS HEPARAN + Intact Endothelium Limits Hemostasis THROMBIN INACTIVATES PAI vFW multimers Subendothelium

15 NOPGI 2 ADPase INHIBITS PLATELET ACTIVATION THROMBOMODULIN PROTEIN C PROTEIN Ca PROTEIN S INACTIVATES Va + VIIIa ATIII INHIBITS Xa + THROMBIN PLASMINOGEN ACTIVATORS (tPA) (uPA) PLASMINOGEN PLASMIN FIBRINOLYSIS HEPARAN + Intact Endothelium Limits Hemostasis – Fibrinolysis THROMBIN INACTIVATES PAI vFW multimers Subendothelium

16 NOPGI 2 ADPase INHIBITS PLATELET ACTIVATION THROMBOMODULIN PROTEIN C PROTEIN Ca PROTEIN S INACTIVATES Va + VIIIa ATIII INHIBITS Xa + THROMBIN PLASMINOGEN ACTIVATORS (tPA) (uPA) PLASMINOGEN PLASMIN FIBRINOLYSIS HEPARAN + Intact Endothelium Limits Hemostasis Protein C System THROMBIN INACTIVATES PAI vFW multimers Subendothelium

17 PGI 2 ADPase INHIBITS PLATELET ACTIVATION THROMBOMODULIN PROTEIN C PROTEIN Ca PROTEIN S INACTIVATES Va + VIIIa ATIII INHIBITS Xa + THROMBIN PLASMINOGEN ACTIVATORS (tPA) (uPA) PLASMINOGEN PLASMIN FIBRINOLYSIS HEPARAN + Intact Endothelium Limits Hemostasis - Chemical Mediators THROMBIN INACTIVATES PAI vFW multimers Subendothelium NO

18 Production of Coagulation Factors Synthesized in the liver-Synthesized in the liver- –All except Factor VIII –Vitamin K dependent II, VII, IX, and XII, VII, IX, and X Protein C, Protein SProtein C, Protein S Factor VIII- unknownFactor VIII- unknown

19 Synthesized in liverSynthesized in liver Serine proteases, inactivated by AT3Serine proteases, inactivated by AT3 Activation on surface of biologicActivation on surface of biologicmembranes Have an affinity for binding calciumHave an affinity for binding calcium Vitamin K Dependent Enzymes: Factors II, VII, IX, X

20 Coagulation Cascade- PT TISSUE FACTOR FACTOR VII VIIa (ACTIVATED) ( XI?) IX IXa TFPI VIII FACTOR X Xa V, Ca FACTOR II IIa FIBRINOGEN FIBRIN MONOMERS FACTOR XIII IN VITRO CROSS-LINKED FIBRIN PT (STABLE FIBRIN CLOT) APTT CONTACT ACTIVATOR FXII, FXI, FLETCHER, FITZGERALD FACTORS VIII IX IXa PT PHOSPHOLIPID PLATELET ACTIVATION INHIBITION OF CLOTTING THROMBOMODULIN PROTEIN C (ENDPOINT) PHOSPHOLIPID

21 Coagulation Cascade- APTT TISSUE FACTOR FACTOR VII VIIa (ACTIVATED) ( XI?) IX IXa TFPI VIII FACTOR X Xa V, Ca FACTOR II IIa FIBRINOGEN FIBRIN MONOMERS FACTOR XIII IN VITRO CROSS-LINKED FIBRIN PT (STABLE FIBRIN CLOT) APTT CONTACT ACTIVATOR FXII, FXI, FLETCHER, FITZGERALD FACTORS VIII IX IXa PT PHOSPHOLIPID PLATELET ACTIVATION INHIBITION OF CLOTTING THROMBOMODULIN PROTEIN C (ENDPOINT)

22 Prothrombin Time Poor reproducibility from lab to lab in USPoor reproducibility from lab to lab in US –No good assayed standards –Many manufacturers –Many chemically different reagents –Many different types of instruments –Poor lot-to-lot reproducibility even from same manufacturer

23 Reporting Protime Results Each laboratory must establish its own normal range using the instrument and reagents that it is usingEach laboratory must establish its own normal range using the instrument and reagents that it is using It may have to be redone with each new lot of reagents, certainly, at least rechecked and verified- insist on it from the laboratory you useIt may have to be redone with each new lot of reagents, certainly, at least rechecked and verified- insist on it from the laboratory you use Results should be expressed in seconds, not INRResults should be expressed in seconds, not INR Results should be compared to the normal range. The true Control value is meaningless for clinical use.Results should be compared to the normal range. The true Control value is meaningless for clinical use.

24 Prothrombin Time The INR is the answer to our prayers- Hallelujah- NOT!! The INR is the answer to our prayers- Hallelujah- NOT!! –Poor calibration by reagent manufacturers is the weak link in the chain –Intended only for inter laboratory comparisons in patients who are on steady state anticoagulation with coumadin: at least two weeks of therapy, ambulatory, normal activity and diet –Widely misapplied to express protime results in all other situations

25 Bleeding Time Widely misused as a screening test for platelet function abnormalitiesWidely misused as a screening test for platelet function abnormalities Can predict trends when used to study large populationsCan predict trends when used to study large populations Cannot predict bleeding risk in individual patients - use for this purpose has been discreditedCannot predict bleeding risk in individual patients - use for this purpose has been discredited

26 Screening for Hemostatic Defects PT, APPT- sensitivity is too poor to pick up mild defectsPT, APPT- sensitivity is too poor to pick up mild defects Bleeding time- poorly reproducible, too many false positives and false negatives, Most common cause of a prolonged bleeding time- improperly performedBleeding time- poorly reproducible, too many false positives and false negatives, Most common cause of a prolonged bleeding time- improperly performed Best screen: good historyBest screen: good history

27 Screen for Platelet Abnormalities No good tests, historyNo good tests, history Immediate bleedingImmediate bleeding Mucous membrane bleedingMucous membrane bleeding Easy bruisingEasy bruising PetechiaePetechiae

28 Screen for Clotting Factor Deficiencies Delayed onset of bleedingDelayed onset of bleeding Large ecchymoses or hematomasLarge ecchymoses or hematomas Bleeding into jointsBleeding into joints

29 Screening History for Bleeding Problems Do you think you have a bleeding problem?Do you think you have a bleeding problem? Does anyone in your family have a bleeding problem?Does anyone in your family have a bleeding problem? Easy bruising?Easy bruising? Previous hemostatic challenges:Previous hemostatic challenges: o Major surgery o Trauma o Extraction of impacted teeth

30 Bleeding Problems Bleeding Problems Pre-operative screeningPre-operative screening Patient with suspicious historyPatient with suspicious history Actively bleeding patientActively bleeding patient

31 Pre-operative Screening Most common hereditary bleeding problems?Most common hereditary bleeding problems? Acquired bleeding problems?Acquired bleeding problems? Sensitivity of screening tests?Sensitivity of screening tests?

32 Hereditary Bleeding Disorders von Willebrands disease - plateletvon Willebrands disease - plateletfunction Storage pool disease (delta granule deficiency) - platelet functionStorage pool disease (delta granule deficiency) - platelet function Factor VIII deficiency (Hemophilia A)Factor VIII deficiency (Hemophilia A) Factor IX deficiency (Christmas disease)Factor IX deficiency (Christmas disease) Factor XI deficiencyFactor XI deficiency

33 Patient with Suspicious History Refer to laboratory or specialist that specializes in bleeding disorders.Refer to laboratory or specialist that specializes in bleeding disorders.

34 Actively Bleeding Patient Focal bleeding - catgut insufficiencyFocal bleeding - catgut insufficiency Generalized bleeding -Generalized bleeding - o Thrombocytopenia o Vitamin K deficiencies - common o DIC - most over-diagnosed cause of bleeding in the acute care/ICU setting. Primary fibrinolysis - rare

35 Acquired Bleeding Problems drug-induced platelet function defectsdrug-induced platelet function defects ThrombocytopeniaThrombocytopenia vitamin K deficiencyvitamin K deficiency Liver diseaseLiver disease Coagulation inhibitorsCoagulation inhibitors Post viral Misc. others Idiopathic

36 Vitamin K Deficiency Appropriate clinical setting: a. Poor or no oral intake b. Broad spectrum antibioticsAppropriate clinical setting: a. Poor or no oral intake b. Broad spectrum antibiotics Prolonged PT, PTT with a normal platelet count and fibrinogen - presumptive diagnoses of Vitamin K deficiencyProlonged PT, PTT with a normal platelet count and fibrinogen - presumptive diagnoses of Vitamin K deficiency

37 Acute DIC: A clinical-pathologic Dx Severely, acutely ill patient (not clinically stable).Severely, acutely ill patient (not clinically stable). Decreasing platelet count and/or fibrinogen.Decreasing platelet count and/or fibrinogen.

38 Acute DIC Principles Most over-diagnosed cause of bleeding in a hospital/ICU setting.Most over-diagnosed cause of bleeding in a hospital/ICU setting. Should be approached as a diagnosis of exclusionShould be approached as a diagnosis of exclusion If it is the only diagnosis you can think of, you are over your head. GET HELPIf it is the only diagnosis you can think of, you are over your head. GET HELP Vitamin K deficiency is much more common.Vitamin K deficiency is much more common. Many other factors are more likely to be the cause of thrombocytopenia.Many other factors are more likely to be the cause of thrombocytopenia.

39 Possible DIC Run all tests on the same specimen:Run all tests on the same specimen: PT, PTT, Fibrinogen, FDP Platelets (Factor V, Factor VIII). It may take sequential testing to establish diagnosis.It may take sequential testing to establish diagnosis.

40 Sources of Vitamin K Diet- Fresh, green leafy vegetablesDiet- Fresh, green leafy vegetables Synthesis by bacteria in the intestinal trackSynthesis by bacteria in the intestinal track Typical ICU/acutely ill, hospitalized patientTypical ICU/acutely ill, hospitalized patient –No or poor oral intake –Broad spectrum antibiotic therapy –Increased vitamin K requirement because of illness Result: Acquired vitamin K deficiency within two to three days of admissionResult: Acquired vitamin K deficiency within two to three days of admission

41 Vitamin K Dependent Factors II, VII, IX, XII, VII, IX, X PT - II, VII, XPT - II, VII, X APTT - II, IX, XAPTT - II, IX, X

42 Vitamin K Deficiency vs. Acute DIC Vitamin KDIC PT APT FDP Fibrinogen *Platelets N or prolongedProlonged Normal ProlongedN or prolonged Usually elevated N or decreased Usually decreased

43 Elevated Levels of FDP Recent surgeryRecent surgery Acute thromboembolic eventAcute thromboembolic event Renal failureRenal failure Hepatic failureHepatic failure Acute myocardial infarctionAcute myocardial infarction DICDIC TTP/HUSTTP/HUS Primary fibrinolysisPrimary fibrinolysis

44 Suggested Approach to the Bleeding Hospitalized Patient Draw PT, APTT, FDP, fibrinogen and platelet count on same specimen as a panel. Do not try to use values drawn at different times.Draw PT, APTT, FDP, fibrinogen and platelet count on same specimen as a panel. Do not try to use values drawn at different times. Immediately give Vitamin KImmediately give Vitamin K Redraw panel in 4-6 hours.Redraw panel in 4-6 hours. o K deficiency should show some degree of correction of PT and APTT within this time period o DIC should manifest itself by a decreasing fibrinogen without any significant correction of PT< APTT

45 Diagnostic Approach to Thrombocytopenia Good history; medication - dont forget heparin; Acuteness of onset; Underlying diseases Physical - splenomegaly Examination of blood smear by an experienced individual; platelet morphology, Other hematologic abnormalities Bone marrow examination - almost never helpful in the absence of other hematologic abnormalities


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