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Platelet Function in Cardiothoracic Surgery

Platelet Function in Cardiothoracic Surgery

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Platelet Function in Cardiothoracic Surgery

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  1. Platelet Function in Cardiothoracic Surgery Mike Poullis

  2. Overview • Basic science • What are they? • How do they work? • Methods of assessing platelet function • Full blood count • Microaggregation • Macroaggregation • Thromboelastography (TEG) • Platelet function analyser • Bleeding time • Clinical scenarios • Drugs • Medical conditions • Congenital disorders • Cardiopulmonary bypass • Aprotinin • HIT • On the ward

  3. Basic science • What are they? • How do they work?

  4. What Is a Platelet?

  5. Blood Film

  6. Ultra Structure

  7. Coagulation System • Platelets • Soluble Factors • Red Cells • Soluble factors interact with platelets to form a mesh that RBCs stick to

  8. How Do Platelets Work ? • Afferent pathway • Inside platelet pathway • Efferent pathway Inside platelet pathway Efferent pathway Afferent pathway

  9. Platelet Agonists (Afferent) Agonist Receptor Adrenaline alpha Collagen VLA ADP ADP Thrombin PAR I and IV

  10. The platelet Microaggregation and Macroaggregation

  11. Mechanism of G protein receptor activation by soluble ligand eg ADP Soluble ligand (Reversible) Cell Membrane G protein

  12. Mechanism of G protein receptor activation by protease eg Thrombin Protease eg thrombin (Irreversible) Cell Membrane G protein

  13. (cont) Tethered ligand (Irreversible) Peptide Cell Membrane G protein Activation

  14. PAR activating peptides PAR activating peptide (reversible) Cell Membrane G protein Activation

  15. Actions proteolytic inhibitors eg Aprotinin Protease eg thrombin Aprotinin Cell Membrane G protein

  16. PAR deactivation Protease eg thrombin Deactivator eg elastase aa 43/44 & 55/56 aa 41/42 (Irreversible) NH2 Cell Membrane G protein

  17. Platelet Thrombin desensitisation 1 Neutrophil elastase cleaves PAR-1 Specific cleavage inhibits activation 2 Thrombin fragment deactivation theory

  18. Efferent Agonist Receptor GP IIb/IIIa Fibrinogen GP Ib Von Willebrand Factor

  19. GP IIb/IIIa Cross Linking

  20. Techniques to Understand • Microaggregation • Macroaggregation • Platelet function analysers • Thrombelastography • Calcium fluxes

  21. Microaggregation and How to Count Platelets No No Size Size

  22. Macroaggregation Increasing aggregation Time

  23. Platelet Function Analyser

  24. Thromboelastography (TEG)

  25. Principles of Thrombelastography

  26. Readout

  27. What the Numbers/letters Mean • R: Time from initiation to initial fibrin formation • k: Time of clot formation until amplitude of 20 mm • Alpha angle: Acceleration (kinetics) of fibrin build up and cross-linking • MA - Maximum amplitude strength of clot (number function platelets, fibrin) • MA60: The rate of amplitude reduction 60 min. after MA (stability) of the clot

  28. Tips and Tricks • Heparinase • Adding c7E3 Fab (ReoPro) to the TEG sample will eliminate platelet function from the thromboelastogram. • Antifibrinolytic agents such as Epsilon-Aminocaproic Acid, Tranexamic acid and Aprotinin

  29. Normal Coagulation Profile Heparinase No Heparinase

  30. Heparin Effect Heparinase No Heparinase

  31. General Shapes Of TEGS

  32. Calcium Flux Measurements

  33. Calcium Flux Measurements 1 Thrombin 2 Adrenaline A control B Aprotinin

  34. Tests of Platelet Function • Full blood count • Whole Blood tests • Microaggregation • Thrombelastography • Purified Platelet tests • Microaggregation • Macroaggregation • Platelet function analysers • Calcium flux • Skin bleeding time

  35. Advantages of Techniques • Full blood count • Quick, easy, reproducible, understandable • Whole Blood tests • Microaggregation, Thrombelastography Easy MAJOR ADVANTAGE IS NO SAMPLE PREPERATION • Purified Platelet tests • Microaggregation Easy • Macroaggregation PRECISE DEFECT • Platelet function analysers PRECISE DEFECT • Calcium flux PRECISE DEFECT • Skin bleeding time • Whole body answer

  36. Limitations of Techniques • Full blood count • Number not function • Whole Blood tests • Microaggregation No commercial kit • Thrombelastography?sensitivity • Purified Platelet tests YOU HAVE TO PREPARE THE PLATELETS • Microaggregation No commercial kit • Macroaggregation Experienced technician • Platelet function analysers No enzymes available • Calcium flux Expensive and experience needed • Skin bleeding time • Invasive, not specific

  37. Clinical Scenarios • Drugs • Medical conditions • Congenital disorders • Cardiopulmonary bypass • Aprotinin • HIT • On the ward

  38. Effect of Drugs on Platelet Function • Aspirin (Non steroidal anti inflammatory drugs) • Clopidogrel, Ticlopidine • ReoPro, Tirofiban • Prostacyclin • Hirudin • Ancrod

  39. Aspirin (Non steroidal anti inflammatory drugs) TxA2 Platelet PgI2 Endothelium

  40. Clopidogrel / Ticlopidene

  41. ReoPro / Tirofiban / Integrilin Platelet Platelet GP 11b/111a Fibrin GP 11b/111a

  42. Effect of Drugs on Platelet Function - Cont • Prostacyclin • Hirudin • Ancrod

  43. Medical Conditions • Hyperglobulinaemia • Multiple myeloma and • Waldestrons macroglobulinaemia • Renal failure Uraemia • Liver disease • Myeloproliferative disorders • Essential thrombocythaemia • Polycytheamia • Myelodysplasias

  44. Congenital Platelet disorders • All rare • VonWillibrands (commonest) • Glanzmann Thrombasthenia (Acquired common) • Bernard-Soulier • Platelet storage disorders

  45. Von Willebrands Platelet Factor V111 vWF Endothelium Stabilisation and adhesion

  46. Glanzmann Thrombasthenia • Genetic platelet disorder • Gp IIb/IIIa deficient or dysfunctional • FACS analysis

  47. Bernard-Soulier • Large platelets • Phospholipid not made available • GP 1b deficiency Platelet Storage Disorders • ADP or 5-HT release deficiency • Defect in dense or alpha granules

  48. How are platelets protected during CPB? • Heparin only works on soluble factors!