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Thromboelastography: Applications in Anesthesia

Thromboelastography: Applications in Anesthesia. 10 December 2002. Objectives. Hemostasis Introduction to Thromboelastography (TEG) Examples TEG in Trauma, CT and Obstetrical Anesthesia TEG Advantages/Disadvantages. Hemostasis.

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Thromboelastography: Applications in Anesthesia

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  1. Thromboelastography: Applications in Anesthesia 10 December 2002

  2. Objectives • Hemostasis • Introduction to Thromboelastography (TEG) • Examples • TEG in Trauma, CT and Obstetrical Anesthesia • TEG Advantages/Disadvantages

  3. Hemostasis • A complicated, dynamic process that results in the aggregation of fibrin and platelets to form a clot. • Conventional coagulation studies measure certain endpoints of hemostasis but not the overall process or the strength of the clot.

  4. Conventional Coag Studies “Conventional coagulation screens are frequently inadequate for the purpose of monitoring coagulation…it is theoretically possible to have normal PT and PTT values but still have active bleeding as a result of abnormal hemostasis.” Mallett, S & D Cox. Thromboelastography. British Journal of Anaesthesia, 1992;69:307-13.

  5. Conventional Coag Studies PT, PTT, fibrinogen, platelet count, D-dimer …” have no clinical utility as predictors of clinical bleeding.” Gelb, A. et al. Changes in blood coagulation during and following CPB, lack of correlation with clinical bleeding. American Journal of Clinical Pathology, 1996;106(1):87-99.

  6. Produces a “footprint” or “signature” which gives a global assessment of hemostatic function from initiation of the protein coagulation cascade through clot lysis. Thromboelastography (TEG)

  7. Thromboelastography (TEG) • Developed by Hartert in Germany in 1948 as a research tool. • First used clinically in liver transplantation by Kang in Pennsylvania more than 25 years later. • Widest use in cardiopulmonary bypass (CPB) and liver transplantation. • Other uses: Trauma, Obstetrics, Hypercoagulable states, Surgery, etc.

  8. 0.36 ml whole blood in spinning cup. Pin in blood sample begins to spin when bonded to the fibrin-platelet complex. Measures viscoelastic properties of the clot. Pin movement monitored as an electrical signal. Thromboelastography

  9. TEG Analyzer

  10. Time from sample placement in cup until the tracing amplitude is 2 mm . Represents rate of initial fibrin formation. Functionally related to plasma clotting factor activity. R (reaction) time

  11. Prolongation related to factor deficiencies or inhibitor presence (Tx = FFP). Decreased r-time may be present in hypercoagulable states (Tx = anticoagulation). Normal = 6-8 minutes. R-time (continued)

  12. Measured from R-time to where the tracing amplitude is 20 mm. Represents time to reach a certain level of clot strength. Affected by clotting factors, fibrinogen and platelets. Normal is 3-6 minutes. K (clotting) time

  13. Angle formed by the slope of the tracing from the R-time to the K-time. Represents the speed of clot strengtheningdue to fibrin buildup. Normal is 50-60°. Alpha Angle

  14. Decreased values result from hypofibrogenemia and thrombocytopenia (Tx = cryo +/- platelets). Increased values from hypercoagulable states. Alpha Angle

  15. Reflection of maximal strength of the clot. Normal = 50-60 mm. Decreased values from thrombocytopenia or poorly functioning platelets (Tx = platelets). Increased values from hypercoagulable states. Maximum Amplitude (MA)

  16. The amplitude at 30 minutes after the MA. Represents the stability of the clot. Value >7.5% represents fibrinolysis (Tx = antifibrinolytic agent). A30 or LY30

  17. Examples • GA: 47 yo female with history of HIT & anticardiolipin antibodies, now POD#7 from gastric bypass presented with RUE edema and pain. • Found to have right subclavian vein thrombosis. • Started on hirudin infusion.

  18. Examples • PT=34, PTT=101, INR=3.6, Plt=61

  19. Examples • DG: 64 yo female s/p LUE muscle biopsy for undetermined neuromuscular disorder with subsequent development of necrotizing fasciitis resulting in LUE disarticulation followed by sepsis and ARDS. • Patient was placed on high frequency ventilator with chemical paralysis. • Unable to use heparin or LMWH due to HIT concern…High risk for DVT.

  20. Examples • PT=13, PTT=38, INR=1.0, Plt=86

  21. Examples • MN: 21 yo male sustained multiple stab wounds to chest & abdomen. • Bilateral chest tubes placed for right HTX & left PTX. • 1300 cc blood from right chest tube at time of placement; no further output. • To OR for repair of left diaphragmatic laceration seen on CT scan. • Received 5000 cc LR, 250 cc 5% albumin, 1unit PRBC.

  22. Examples (MN continued) • Returned to SICU with 2400 cc blood output from right chest tube in 60 minutes. • To OR for right exploratory thoracotomy resulting in RLL wedge resection, repair of right diaphragmatic laceration with underlying liver laceration. • Received 7000 cc LR, 2000 cc NS, 6 units PRBC, 4 units FFP, 1190 cc cell saver, 250 cc 5% albumin.

  23. Examples • PT=23, PTT=43, INR=2.2, Plt=38 • Given 4 units FFP, 12 units plt, 10 units cryo after TEG/coag studies.

  24. Examples • GT: 75 yo female with severe MR underwent mitral annuloplasty with OR course complicated by inominate vein bleeding with urgent Fem-Fem CPB. • Total CPB time = 5 hours. • Received 11 units PRBC, 12 units FFP, 24 units Platelets, 2000 cc cell saver, 8000 cc LR, 1000 cc 5% albumin. • Aprotinin infusion at 50 cc/hr.

  25. Examples • PT=32.1, PTT=91, INR=3.3, Plt=84, Fib=109, D-dimer=2.01 (0-0.5) • 4 units FFP, 10 units cryo, 6 units platelets.

  26. Examples • Obstetrical patient in DIC.

  27. Technique • “2 or 3 syringe” technique for drawing blood. • Blue-top tube if not POC. • 4 minutes from blood draw to cuvette for best results. • Add activator (TF, celite) for faster results. • Add heparinase if sample is heparinized. • Add 0.2 M CaCl if sample citrated (blue-top).

  28. TEG in the Austere Environment • POC test can be done without reagent. • Can be performed in any climate. • Haemoscope weighs 6 kg. • Compact: can use with laptop or keyboard/screen available from the manufacturer.

  29. TEG in Trauma Kaufman, C. et al. Usefulness of thromboelastography in assessment of trauma patient coagulation. Journal of Trauma, 1997;42(4):716-22. • “Exsanguination is second only to central nervous system injuries as a cause of trauma death.” • “The control of hemorrhage has been identified as a priority in modern trauma patient care, second in importance only to adequate ventilation.”

  30. TEG in Trauma: Study • 69 adult patients with blunt injuries. • Platelet count, PT/PTT, and TEG drawn in trauma suite. • Clinicians providing care blinded to TEG results to avoid effect on transfusion decisions. • 52 patients demonstrated coagulation abnormalities by TEG; 45 were hypercoagulable (mean ISS, 13.1), 7 were hypocoagulable (mean ISS, 28.6).

  31. TEG in Trauma: Results • 2 of 45 hypercoagulable patients transfused in first 24 hours. • 6 of 7 hypocoagulable patients transfused in the first 24 hours. • 0 of 17 with normal TEG transfused.

  32. TEG in Trauma: Conclusion • Logistic regression of ISS, RTS, PT/PTT, and TEG on use/nonuse of blood products within the first 24 hours demonstrated that only ISS (p<0.001) and TEG (p<0.05) are predictive of transfusion within the first 24 hours. • ISS is a more powerful predictor but not as readily available as TEG.

  33. TEG in CT Anesthesia: Study Shore-Lesserson, L. et al. Thromboelastography-guided transfusion algorithm reduces transfusions in complex cardiac surgery. Anesth Analg 1999;88:312-9. • Patients randomly assigned to either TEG-guided transfusion algorithm (n=53) or routine transfusion therapy (n=52) after CPB. • Coagulation tests, TEG, mediastinal tube drainage, and transfusion amounts compared at multiple time points.

  34. TEG in CT Anesthesia: Results • No difference in intraoperative transfusion rates. • Significantly less post-op and total transfusion in TEG group: Overall incidence of non-RBC transfusion 7/53 (13%) in TEG group vs 17/52 (33%) in control (p < 0.02). • Mediastinal tube drainage not statistically different at 6, 12 or 24 hours post-op.

  35. TEG in CT Anesthesia: Conclusions • TEG is a point-of-care (POC) test with intitial results available in 10-15 minutes vs PT/PTT available in 30-45 minutes. • Normal TEG results forestalled ordering blood products. The majority of products were given in the ICU when the algorithm was no longer enforced. • Patients are often transfused before lab test results are available.

  36. TEG in OB Anesthesia: Study Orlikowski, C. et al. Thrombelastography changes in pre-eclampsia and eclampsia. British Journal of Aneaesthesia 1996; 77:157-161. • 49 patients with pre-eclampsia or eclampsia. • 18 patients with PC <150. • 7 patients with PC < 100.

  37. TEG in OB Anesthesia: Results • TEG variables k-time and MA had strong correlation with PC. • PC:K r P <150 -0.68 0.003 <100 -0.84 0.02 • PC:MA r P <150 0.72 0.001 <100 0.78 0.04

  38. TEG in OB Anesthesia: Results • No correlation between bleeding time and thrombocytopenia or any TEG variable. • In 10 patients with adequate PC but prolonged bleeding time, TEG variables were all normal suggesting normal hemostasis. • No patient with PC < 100, prolonged bleeding time or abnormal TEG received a regional anesthetic.

  39. TEG in OB Anesthesia: Conclusions • MA of 53 correlated with PC of 54 (CI=40-75). • Patient with PC > 75 should not have regional anesthesia denied (Upper limit of 95% CI). • Insufficient data to recommend TEG without PC. • TEG has greatest promise in pre-e/e patient with PC < 100. • Bleeding time is “particularly unhelpful.”

  40. TEG Disadvantages • Will not identify presence of specific inhibitor/activator or factor deficiency. • Best technique is 4 minutes from blood draw to cuvette—avoided with POC testing. • Time to results?? • More testing/verification studies/experience is needed.

  41. TEG Advantages • Quick results with use of activator. • Point-of-care test available without reagent. • Economical * Fewer tests * Fewer transfusions (Adverse reactions, immunological complications, infectious risks, cost, supply shortage, etc). • Multiple applications: Trauma, OB, CT, Regional, ICU, LMWH, 6% HES, etc.

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