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Thromboelastography
The document discusses thromboelastography (TEG), a technique for assessing whole blood coagulation. TEG monitors the viscoelastic properties of clotting blood to evaluate clot formation, kinetics, strength and stability. It provides a global assessment of hemostasis and can detect coagulation factor deficiencies, platelet issues and fibrinolysis. TEG results are rapid and help guide treatment, unlike conventional coagulation tests which examine isolated parts of the clotting process. Measurements from a TEG tracing include r and k times, alpha angle, maximum amplitude and lysis parameters. TEG gives useful qualitative and quantitative analysis of hemostasis.
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Thromboelastography
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- 3. • In surgerywe have to manage patients with a bleeding diathesis in the preoperative, intraoperative or postoperative period.
- 4. • Complex surgicalprocedures including cardiac and liver surgery are associated with a potential for significant perioperative blood loss and the development of post operative bleeding disorders.
- 5. • inherent risksof the use of homologous blood and blood products, and allied to the scarcity of these resources, make it important that treatment with blood products is based on scientific evidence of need.
- 6. • A varietyof coagulation tests are used to assess whole blood coagulation.
- 7. COAGULATION MONITORING Conventionaltests •Tests of coagulation *Platelets • number • function *Clotting studies • PT • APTT *Fibrinogen levels •Tests of fibrinolysis * degradation products
- 8. • Each ofthese tests measures a different aspect of the clotting process, but even in combination they do not provide a complete picture of the status of the coagulation system
- 9. • Besides evaluationof platelet function remains insensitive and time consuming. The platelet count provides only a quantitative, not qualitative index of platelet status.
- 10. • At presentthe treatment of postoperative bleeding remains empirical because of the perceived need for immediate correction of the haemostatic defect and lack of readily available measures of all phases of clot formation and breakdown , including the strength of the clot • FFP and platelets often given with little scientific basis.
- 11. What we need? an effective and convenient means of monitoring whole blood coagulation which evaluates the elastic properties of whole blood and provides a global assessment of heamostatic function.
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- 13. • First developedby Dr. Hellmut Hartet at University of Heidelberg, School of Medicine in 1948 as a method to assess global haemostatic function from a single blood sample; this was the original thromboelastography
- 14. WHAT IS THROMBOELASTOGRAPHY Functional Description • Thromboelastography monitors the thrombodynamic properties of blood as it is induced to clot under a low shear environment resembling sluggish venous flow. The patterns of change in shear-elasticity enable the determination of the kinetics of clot formation and growth as well as the strength and stability of the formed clot.
- 15. • The strengthand stability of the clot provide information about the ability of the clot to perform the work of haemostasis, while the kinetics determine the adequacy of quantitative factors available to clot formation
- 16. • In classicalthrombelastography, a small sample of blood (typically 0.36 ml) is placed into a cuvette (cup) which is rotated gently through 4º 45´ (cycle time 6/min) to imitate sluggish venous flow and activate coagulation. When a sensor shaft is inserted into the sample a clot forms between the cup and the sensor. The speed and strength of clot formation is measured in various ways (now usually by computer)
- 19. • The patternsof changes in strength and elasticity in the clot provide information about how well the blood can perform hemostasis (the halting of blood flow), and how well or poorly different factors are contributing to clot formation.
- 20. THROMBOELASTOGRAPHY Basic Principles • Heated (37C) oscillating cup • Pin suspended from torsion wire into blood • Development of fibrin strands “couple” motion of cup to pin • “Coupling” directly proportional to clot strength • tension in wire detected by EM transducer
- 21. THROMBOELASTOGRAPHY Basic Principles • Electrical signal amplified to create TEG trace • Result displayed graphically on pen & ink printer or computer screen • Deflection of trace increases as clot strength increases & decreases as clot strength decreases
- 24. THROMBOELASTOGRAPHY Refinements toTechnique • TEG accelerants / activators / modifiers • Celite / Kaolin / TF accelerates initial coagulation • Reopro (abciximab) blocks platelet component of coagulation • Platelet mapping reagents modify TEG to allow analysis of Aspirin / Clopidigrol effects • Heparinase cups • Reverse residual heparin in sample • Use of paired plain / heparinase cups allows identification of inadequate heparin reversal or sample contamination
- 25. THROMBOELASTOGRAPHY The “r”time r time •represents period of time of latency from start of test to initial fibrin formation •in effect is main part of TEG’s representation of standard”clotting studies” •normal range • 15 - 23 mins (native blood) • 5 - 7 mins (kaolin-activated)
- 26. THROMBOELASTOGRAPHY What affectsthe “r” time? •r time by • Factor deficiency • Anti-coagulation • Severe hypofibrinogenaemia • Severe thrombocytopenia •r time by • Hypercoagulability syndromes
- 27. THROMBOELASTOGRAPHY The “k”time k time •represents time taken to achieve a certain level of clot strength (where r time = time zero ) - equates to amplitude 20 mm •normal range • 5 - 10 mins (native blood) • 1 - 3 mins (kaolin-activated)
- 28. THROMBOELASTOGRAPHY What affectsthe “k” time? •k time by • Factor deficiency • Thrombocytopenia • Thrombocytopathy • Hypofibrinogenaemia •k time by • Hypercoagulabili ty state
- 29. THROMBOELASTOGRAPHY The “”angle angle •Measures the rapidity of fibrin build-up and cross-linking (clot strengthening) •assesses rate of clot formation •normal range • 22 - 38 (native blood) • 53 - 67(kaolin-activated)
- 30. THROMBOELASTOGRAPHY What affectsthe “” angle? • Angle by • Hypercoagulable state • Angle by • Hypofibrinogenemia • Thrombocytopenia
- 31. THROMBOELASTOGRAPHY The “maximumamplitude” (MA) Maximum amplitude •MA is a direct function of the maximum dynamic properties of fibrin and platelet bonding via GPIIb/IIIa and represents the ultimate strength of the fibrin clot •Correlates to platelet function • 80% platelets • 20% fibrinogen •normal range • 47 – 58 mm (native blood) • 59 - 68 mm (kaolin-activated)
- 32. THROMBOELASTOGRAPHY What affectsthe “MA” ? •MA by • Hypercoagulable state •MA by • Thrombocytopenia • Thrombocytopathy • Hypofibrinogenemia
- 33. THROMBOELASTOGRAPHY Fibrinolysis •LY30 •measures % decrease in amplitude 30 minutes post-MA •gives measure of degree of fibrinolysis •normal range • < 7.5% (native blood) • < 7.5% (celite-activated) •LY60 • 60 minute post- MA data
- 34. THROMBOELASTOGRAPHY Other measurementsof Fibrinolysis •A30 (A60) • amplitude at 30 (60) mins post-MA •EPL •earliest indicator of abnormal lysis •represents “computer prediction” of 30 min lysis based on interrogation of actual rate of diminution of trace amplitude commencing 30 secs post-MA •early EPL>LY30 (30 min EPL=LY30) •normal EPL < 15%
- 35. THROMBOELASTOGRAPHY What measurementsare affected by fibrinolysis? •Fibrinolysis leads to: • LY30 / LY60 • EPL • A30 / A60
- 36. THROMBOELATOGRAPHY Quantitative analysis • Clot formation – Clotting factors - r, k times • Clot kinetics – Clotting factors - r, k times – Platelets - MA • Clot strength / stability – Platelets - MA – Fibrinogen - Reopro-mod MA • Clot resolution – Fibrinolysis - LY30/60; EPL A30/60
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- 38. TEG v CONVENTIONALSTUDIES • Conventional tests • test various parts of coag cascade, but in isolation • out of touch with current thoughts on coagulation • plasma tests may not be accurate reflection of what actually happens in patient • difficult to assess platelet function • static tests • take time to complete best guess or delay treatment • TEG • global functional assessment of coagulation / fibrinolysis • more in touch with current coagulation concepts • use actual cellular surfaces to monitor coagulation • gives assessment of platelet function • dynamic tests • rapid results rapid monitoring of intervention
- 39. Advantages of TEGover conventional coagulation monitoring • It is dynamic, giving information on entire coagulation process, rather than on isolated part • It gives information on areas which it is normally difficult to study easily – fibrinolysis and platelet function in particular • Near-patient testing means results are rapid facilitating appropriate intervention • It is cost effective compared to conventional tests
- 40. ROTEM • Rotationalthromboelastography uses a modification of TEG, signal of the pin is transmitted using an optical detecter instead a torsion wire. • Movement orginates from pin and not the cup • Uses an electronic pippette which improves reproducibility and performance
- 41. • In ROTEMthe sensor shaft rotates rather tha the cup • avoids limitations of traditional instruments esp. susceptibility to mechanical shocks and vibrations. • However TEG is rated as the best compromise between usability, usefulness and cost as compared to ROTEM
- 43. SONOCLOT • Sonoclotincorporates a very sensitive visco-elastic detection system which is very sensitive to the changes in the developing clot. It gives more detailed information as compared to Thromboelastograph
- 44. • PRINCIPLE measuresthe changing impedence to movement imposed by the developing clot on a small probe vibrating at an ultrasonic frequency in a coagulating blood sample.
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