Lec 16%Hemostasis&Control (6).ppt

Perfusion Program Outline a.Hemostasis b.platelets c. Coagulation Factors d.Fibrinolysis e.Control Mechanisms: Protein C/ protein S f. Tissue factor g.ATIII h.Kinin Mechanism i. Complement j. SIRS k.CPB effect on hemostasis l. Contact activation in CPB Vascular Fibrinolysis Kinin Generation...

Perfusion Program Outline a.Hemostasis b.platelets c. Coagulation Factors d.Fibrinolysis e.Control Mechanisms: Protein C/ protein S f. Tissue factor g.ATIII h.Kinin Mechanism i. Complement j. SIRS k.CPB effect on hemostasis l. Contact activation in CPB Vascular Fibrinolysis Kinin Generation Platelets Hemostasis Plasma Coagulation Complement Inhibitors Steps of Hemostasis Vascular System • Endothelial damage • Activation of platelets • Activation of plasma coagulation • Release of inhibitors • Initiation of fibrinolysis Platelets Unactivated • • • • • Activated Discoid shape Approximately 2-4 microns in diameter Circulating life, approximately 9-12 days Approximately 1/3 of platelets sequestered in spleen Early responders to vascular damage Platelet Formation • Megakaryocyte – Large precursor cell – Normally present only in bone marrow – Multiple nuclei – Platelets bud from cell cytoplasm – Squeeze through the marrow sinusoids into peripheral circulation Normal Platelets Wrights stain film EM cross section Platelet Activation Platelets Collagen Exposure Release Adherence ADP TXA2 Vascular Injury & Endothelial Damage In Presence of vWF Aggregation Thrombin Platelet Plug Serotonin PF3-Platelet Factor 3 Vasoconstriction Plasma Coagulation Coagulation Factors • Synthesized by liver – except for a portion of Factor VIII (endothelium and megakaryocytes) • Roman Numeral Designation (except for HMWK and PK) • Sub-letter “a” indicates active form • Function as: – cofactors (V and VIII) – enzymes (active form) – substrate (Fibrinogen or Factor I) • End result of their interaction leads to fibrin formation The Coagulation Cascade Extrinsic Tissue Factor + VII Intrinsic XII TF-VIIa PL XI XIIa Common Pathway X XI HMWK XIa II IXa PK PL VIIIa Xa XIII Va Thrombin (IIa) Fibrinogen XIIIa Fibrin Clot Thrombin Thrombin • Fibrinogen to Fibrin • Regulates coagulation reactions – Factors V and VIII – Factor XI • Platelet Activation So How Does Hemostasis Really Work? or Who was John Hageman and why didn’t he bleed? John Hageman • 37-year-old railroad brakeman presented for surgery in 1955 • Routine pre-operative testing revealed a prolonged clotting time • No history of bleeding despite previous tonsillectomy, dental extraction, and assorted injuries • Factor XII deficiency identified by Dr. Oscar Ratnoff • Died in 1968 from a pulmonary embolism following fractures from work related injury Normal Hemostasis • Formation of a platelet aggregate • Molecular level: interaction of coagulation factors takes place on the surface of activated platelets • The Tissue Factor–FVIIa complex: the physiological activator of normal hemostasis Normal Hemostasis (Cell-based Model) II X TF VIIa Xa IIa Va VIIIa TF-Bearing Cell TF VIIa IXa Ca++ V IX X VIII/vWF Va Platelet Ca++ II Xa Va IXa VIIIa Activated Platelet IIa Fibrinogen Hoffman et al. Blood Coagulation & Fibrinolysis 1998;9(suppl 1):S61. Fibrin Fibrinolysis Plasminogen Extrinsic: t-PA, urokinase Activation Intrinsic: factor XIIa, HMWK, kallikrein Exogenous: streptokinase Fibrin, fibrinogen Plasmin Fibrin, fibrinogen degradation products Goals for Anticoagulation • Prevent thrombus formation • Preserve patient’s hemostatic elements • Prevent Systemic Inflammatory Response Control Mechanisms What keeps your arm from clotting off when you cut your finger? Protein C and S • • • • Vitamin K required for synthesis Protein C: major physiological inhibitor of coagulation Protein S: cofactor for Protein C Protein C/S in presence of thrombin forms Activated Protein C (APC) – Inactivates Factors Va and VIIIa – Inhibits activation of factors X and II • Protein C/S deficiency: – 2 to 3 % of general population – Clinical manifestations: • Deep venous thrombosis • Pulmonary embolism • Homozygous Protein C deficiencyneonatal purpura fulminans • Warfarin-induced skin necrosis following warfarin initiation in Protein C deficiency Protein S Tissue Factor Pathway Inhibitor II X TF VIIa Xa IIa Va VIIIa TF-Bearing Cell TF VIIa IXa TFPI V IX X Ca++ Va Platelet Ca++ II Xa Va IXa VIIIa Activated Platelet • TFPI/FXa complex inhibits TF/FVIIa • Direct inhibitor of FXa VIII/vWF IIa Fibrinogen Fibrin Hoffman et al. Blood Coagulation & Fibrinolysis 1998;9(suppl 1):S61. Antithrombin III • Synthesized by liver and endothelial cells • Binds and inhibits Thrombin (IIa) and active clotting Factors Xa, IXa, XIa • Heparin increases the activity of AT III by several thousand-fold • Congenital ATIII deficiency is a rare disorder (<1% of the general population) – increased risk of venous thrombosis – onset of clinical manifestations typically appear in young adulthood. • Acquired ATIII deficiency – – – – – acute thrombosis DIC liver disease nephrotic syndrome oral contraceptive use Antithrombin III XII Tissue Factor + VII TF-VIIa XI PL XI XIIa ATIII X XIa ATIII IXa ATIII II PL PL VIIIa Xa XIII Va ATIII Thrombin (IIa) ATIII Fibrinogen XIIIa Fibrin Kinin Mechanism Inflammatory response and wound healing Negatively Charged Surfaces Factor XII • • • • • • Increased vascular permeability Vasodilatation Smooth muscle contraction Inflammation, phagocytosis Pain Tissue Repair Factor XIIa Factor XIIa Fragments HMWK Kallikrein Bradykinin Prekallikrein Complement • Cascade of enzymatic reactions • Complement activation – Foreign substances (bacteria & viruses) – Components of the cardiopulmonary bypass system – Materials used in the collection and processing of autologous blood – Damaged red blood cells blood recovered from the operative site for autotransfusion • Activation results in: – Macromolecular attack complex – Cell destruction and inflammatory response Systemic Inflammatory Response (SIRS) • Hemostasic Mechanism balance tipped • Activation of cellular and humoral pathways – Plasma coagulation/fibrinolysis – Complement activation & kinin generation – Activation of platelets and leukocytes • Results in a whole body or systemic inflammatory response with disorders of: – Microcirculation – Organ perfusion • Without intervention: – Multiple organ dysfunction – Death • SIRS may occur in: – – – – Sepsis CPB Severe trauma Burns SIRS • • • • • • • • Exposure of blood to artificial surfaces Surgical trauma Ischemia-reperfusion injury, Hypothermia Endotoxin release Platelet activation Whte blood cell activation Generation of reactive oxygen species ti-step model of leukocyte interaction with inflamed vascular endothelium. d endothelium expresses P-selectin and E-selectin that binds PSGL-1 expressed on leukocytes, diating – A: “attachment” and B: “rolling”. L-selectin participates in leukocyte recruitment at sites mmation by mediating “secondary rolling” (leukocyte on leukocyte) through its interaction with PSGL-1. ion” of integrins due to chemokines such as IL-8 results in D: “firm adhesion” of leukocytes to elium via binding of LFA-1 and Mac-1 to ICAM-1. Finally E: “extravasation” occurs. nt leukocytes move towards endothelial cell junctions and igrate into the extracellular matrix with interaction involving PECAM-1 and ICAM-2. platelet selectin glycoprotein-1 phocyte function antigen-1 -1 glycoprotein adhesion molecule-1 Platelet endothelial adhesion molecule-1 CPB Effects on Hemostasis • Hemodilution • Hypothermia • Factor VII/Tissue Factor activation • Contact activation (Factor XII) • Kinin Generation • Activation of complement & systemic inflammatory response • Shear stress (platelet activation) • Fibrinolysis • Anticoagulation/reversal Do we care about Factor XII? In cardiac surgery we certainly do! Contact Activation in CPB Negatively Charged Surface Plasma Coagulation HMWK Factor XII Factor XIIa Kallikrein Plasminogen Prekallikrein Impaired Platelet Function Plasmin Bradykinin Fibrinolysis Complement Activation Systemic Inflammatory Response Solutions to SIRS • Bio-compatible CPB circuit (heparin bonded circuits) • Removing activated neutrophils (leukodepletion filters) • Pharmaceutical drugs (glucocorticoids, complement inhibitors and aprotinin). Heparin Bonded Circuits • Improves the biocompatibility of extracorporeal circuits • Enabled reductions in the dosage of heparin • Large doses of heparin given during CPB are associated with deranged platelet function through activation of GP IIb/IIIa receptors, expression of P-selectin, and enhanced platelet aggregation Heparin Bonded Circuits Reduces all of the following: •neurocognitive dysfunction •complement activation •transfusion requirements •ischemic myocardial damage •pro-inflammatory cytokine production •thrombin, fibrinogen and bradykinin generation Leukocyte filters • AKA leukocyte depleting filters in CPB circuit • Activated monocytes and neutrophils play a significant role in the development of SIRS after CPB and • reduced circulating activated leucocytes • Decrease transfusion requirements • Decreased renal dysfunction • Decreased pulmonary inflammation leading to expedited extubation Glucocorticoids • Shown to reduce levels of pro-inflammatory (hydrocortisone, Methylprednisolone) • Reduce cytokines (TNF-a, IL-6, IL-8) • Enhance release of anti-inflammatory cytokines (IL-10) • Reduce complement activation • Decrease neutrophil integrin CD11b/CD18 (Mac-1) Complement inhibitors • Pexelizumab is a recombinant antibody fragment that binds to the C5 complement component thereby blocking the generation of C5a • statistically significant reduction in risk of MI or death 30 days after surgery