Management of the Bleeding Patient Dr. Alan Tinmouth Director, Adult Regional Hemophilia and Bleeding Disorders Clinic February 1st, 2005

Outline Review the mechanism of blood coagulation Understand the tests used in the investigation of bleeding disorders Understand the therapeutic options in the management of bleeding patients “Hemostasis” Poker

Overview of Hemostasis

Primary Hemostasis: Platelets Adhesion Platelet glycoprotein Ib/V/IX adheres to subendothelium  binding is primarily to vWF Activation Shape change  formation of pseudopods Anionic phospholipids (phospatidylserine and phosphoethanolamine) exposed on external membrane Glycoprotein IIb/IIIa exposed on surface Secretion of platelet granules Aggregation Platelets bind to each other via Gp IIb/IIIa receptor and soluble fibrinogen and vWF  FORMATION OF HEMOSTATIC PLUG

Platelet Adhesion and Activation

Platelet Aggregation

Secondary Hemostasis: Coagulation Factors Coagulation factors are proteins that circulate primarily in inactive state (proenzyme), which are converted to active enzyme Activation of coagulation factors is a stepwise process of one activated factor activating subsequent factor(s) Historically separated into the intrinsic pathway and extrinsic pathway Intrinsic and extrinsic pathways believed to act independently and lead to formation of fibrin clot through separate “coagulation cascades” Model fails to explain many coagulation abnormalities seen clinically

Coagulation in a test tube XII XIIa XI XIa VIIa VII IX IXa +TF INTRINSIC EXTRINSIC +VIIIa X Xa +Va II IIa Fibrinogen Fibrin COMMON

Initiation Phase Tissue factor is spark initiating coagulation cascade Exposed TF activates factor VII Factor VIIa:TF activates Factor VII*, Factor X*, Factor IX* Factor Xa with Va generates a small amount of thrombin II IIa X Xa TF VIIa Va TF-Bearing Cell TF VIIa IX IXa * Vitamin K dependent clotting factors

Amplification Phase II Factor VIIa:TF inactivated by Tissue Factor Pathway Inhibitor (TFPI):Factor Xa complex Thrombin* (II) generated on TF-bearing cell activates platelets and coagulation factors (V, VII*, XI) II IIa VIII/vWF TFPI Xa Xa TF VIIa VIIIa Va TF-Bearing Cell XI XIa V Va Platelet VIIIa Va XIa Activated Platelet * Vitamin K dependent clotting factors

Propagation Phase II IIa Activated platelets serve as phospholipid platform for generation of large amounts of thrombin Factor IXa with VIIIa (+ Ca2+) [tenase] activates factor X Factor Xa with Va (+ Ca2+) [pro-thrombinase] produces large thrombin burst Thrombin then generates fibrin and fibrin clot TF-Bearing Cell TF VIIa IX II IXa X Xa IIa IXa VIIIa Va XIa Activated Platelet IX

Formation of Fibrin Clot: Fibrin Deposition Thrombin binds to fibrinogen and forms fibrin Cleaves fibrinopeptide A and B to leave fibrin monomer Thrombin activates factor XIII to XIIIa, Factor XIIIa catalyzes cross-linking of fibrin monomers to produce stable clot IIa IIa

Coagulation Factor Pathway in Vivo

Fibrinolysis Dissolution of clots needed to maintain vessel patency Fibrin clots are temporary scaffolding that allow for cellular wound healing Dissolution of clots needed to maintain vessel patency Plasmin (converted from plasminogen) is primary agent of fibrinolysis Fibrinolysis is controlled by Activators of plasminogen activation Inhibitors of plasminogen activation Inhibitors of plasmin

Fibrinolysis and Plasmin Inhibition Plasminogen and t-PA bind to fibrin lysine sites Activated plasmin protected from degradation by alpha2-antiplasmin Plasmin optimally positioned to degrade fibrin Plasmin Inhibition Circulating plasmin is rapidly inactivated by alpha2-antiplasmin Prevents systemic (widespread) fibrinolysis Thrombin activated fibrinolytic inhibitor (TAFI) removes lysine sites from fibrin to downregulates fibrinolysis during initial clot formation

Fibrinolytic System

Laboratory Investigations

Platelet Disorders Platelet Count Platelet Morphology (blood film) Platelet Aggregation / Release von Willebrand Studies von Willebrand Antigen Ristocetin Cofactor von Willebrand Multimers Bleeding Time

Coagulation Factor Disorders Prothrombin Time / International Normalized Ratio Activated Partial Thromboplastin Time Thrombin Time 50:50 Mixing Studies Coagulation Factor Assays

Prothrombin Time / International Normalized Ratio Tests for deficiencies or inhibitors of factor VII (a.k.a. extrinsic pathway) Also deficiencies or inhibitors of fibrinogen, prothrombin, IX, X Method Tissue thromboplastin (tissue factor and phospholipid source) is added to recalcified citrated plasma  time to clot measured Different sources of thromboplastin alter the PT  reported as an INR which adjusts for the different sensitivities of the thromboplastins Other Specific Uses Monitor warfarin (oral anticoagulant) therapy

Activated Partial Thromboplastin Time XII XIIa XI XIa VIIa VII IX IXa +TF INTRINSIC EXTRINSIC +VIIIa X Xa +Va II IIa Fibrinogen Fibrin COMMON

Activated Partial Thromboplastin Time Tests for deficiencies or inhibitors of factors VIII, IX, XI and XII (a.k.a. intrinsic pathway) Reduced activity of fibrinogen, prothrombin or factor V or X prolongs the aPTT but the PT/INR is more sensitive Method Test initiated by recalcifying plasma that has incubated with an activator (eg. kaolin) and phospholipid  time to clot formation is measured Other Specific Uses monitor standard heparin therapy screen for lupus anticoagulants / antiphospholipid antibodies

Activated Partial Thromboplastin Time XII XIIa XI XIa VIIa VII IX IXa +TF INTRINSIC EXTRINSIC +VIIIa X Xa +Va II IIa Fibrinogen Fibrin COMMON

Thrombin Time (TT) Tests for deficiencies or dysfunction of fibrinogen Prolonged in the presence of heparin, low or abnormal fibrinogen, and fibrinogen/fibrin degradation products Method Thrombin added to plasma and the time to clot (the rate of conversion of fibrinogen to fibrin) is measured Uses Detect low fibrinogen levels, abnormal fibrinogen or inhibitors of fibrin/fibrinogen

Thrombin Time (TT) XII XIIa XI XIa VIIa VII IX IXa X Xa II IIa +TF INTRINSIC EXTRINSIC +VIIIa X Xa +Va II IIa Fibrinogen Fibrin COMMON

Fibrinolytic System Euglobulin Lysis Alpha 2 Antiplasmin Factor XIII levels

Therapy

Platelet Transfusions - Products Random Donor Platelets Separated from whole blood donations Dose = 5 units (250-300 mls) ABO matched preferable but not mandatory Increases platelet ct by 5-10 x 109/L per unit Single Donor Platelets Collected from 1 donor by apheresis Equivalent to 5-6 random donor platelets Decrease donor exposure Can be matched if patient has identified antibodies to platelets (alloimmune platelet refractoriness)

Indications for Platelet Transfusions Thrombocytopenia Platelet Dysfunction Congenital Acquired Therapeutic Plat ct < 50x109/L Plat dysfunction Prophylactic Prior to invasive procedures Plat ct < 50-100x109/L Prevent spontaneous bleeding Plat ct  10x109/L

Fresh Frozen Plasma Bleeding or Emergency procedure or operation Made from whole blood within 8 hrs of collection Contains all coagulation factors Minimum factor VIII level of 0.7 IU/ml 200-250 mls / unit Effect may only last 4 hrs (t1/2 of factor VII) Indications: INR / PTT > 1.5 x normal and Bleeding or Emergency procedure or operation

Fresh Frozen Plasma Dose: 10-15 ml/kg for bleeding patients Sufficient to increase all individual coagulation factors by 30% (minimum hemostatic level) 5-7 ml/kg may be sufficient for warfarin reversal Alternatives Vitamin K 2 mg will correct INR in 12 -24 hrs No effect on PTT (factors VIII, IX, XI) Oral dose more effective than subcutaneous Intravenous associated with anaphylactic reactions

Cryoprecipitate Precipitate collected from plasma thawed at 40C 10-15 mls/unit Contains specific clotting factors from plasma Factor VIII Fibrinogen von Willebrand’s Factor Factor XIII Indications Fibrinogen < 1.0 g/L Dysfibrinogenemia

Cryoprecipitate Dose 1 unit / 5-10 kg body weight (total 8-10 units) t ½ of 3-5 days Alternatives Factor VIII or IX Deficiency recombinant factor VIII or IX Von Willebrand’s Disease virally inactivated plasma derived factor concentrates Other factor deficiencies recombinant factor concentrates

DDAVP Synthetic vasopressin Release of VIII and vWF from endothelium May also help with platelet dysfunction 2-3 fold rise in levels Dose – 0.3 ug/kg q 12-24 hours Tachyphylaxis may occur after 2-3 doses

Antifibrinolytics Tranexamic acid (Cyclokapron) 20-25 mg/kg po or 10 mg/kg IV q8h Epsilon aminocaproic acid (Amicar) 50-60 mg/kg po q6h Competitive inhibition with plaminogen activator (t-PA) Prevents fibrinolysis (clot breakdown) Promotes thrombosis Relative contraindication in renal bleeding

Recombinant Factor VIIa Initiates coagulation by interaction with TF Only approved for treatment of hemophilia with inhibitors Treat/prevent bleeding in other patient groups? Efficacy not proven Risk of thrombosis? Primary use is bleeding patients refractory to other treatments Dose for hemophilia 90 ug/kg q2-3h Lower dose often effective in other patients 30-40 ug/kg Vials of 1.2 mg, 2.4mg, 4.8mg Cost ~ $1000/mg

“Hemostasis” Poker

One-of-a-Kind INR aPTT TT/Fib Platelets Disorders  N N  N  N  Liver disease Vit K def Coumadin Factor VII N  Heparin Antiphospholipid Ab Factor VIII, IX, XI von Willebrand’s (Factor XII) N  Hypofibrinogenemia Dysfibrinogenemia Thrombin Inhibitors Heparin N  ITP TTP/HUS Drugs Bone Marrow Splenomegaly

Pair INR aPTT TT/Fib Platelets Disorders  N Factor II, V, X, Coumadin Overdose

Three-of-a-Kind INR aPTT TT/Fib Platelets Disorders   N Liver disease (acute)

Full House INR aPTT TT/Fib Platelets Disorders   Liver disease (chronic) DIC

Nothing Von Willebrand’s Disease Mild Hemophilia A or B Mild Factor XI deficiency Platelet Function Disorder Factor XIII deficiency Alpha 2 antiplasmin deficiency Plasminogen Activator Inhibitor deficiency