Thromboelastography

Aka: Thromboelastography, TEG, Viscoelastic Assay, Rotational Thromboelastography, ROTEM, Viscoelastic Substances, Thromboelastography Panel, Activated Clotting Time, Rapid Thromboelastography, r-TEG, rTEG, R-Time, K-Time, Ly30, Lysis Time, Estimated Percent Lysis, Alpha angle

1. See Also
   1. Massive Blood Transfusion
   2. Hemorrhagic Shock
2. Indications
   1. Massive Hemorrhage related transfusions
      1. May assist in determining ratio of Red Blood Cell Transfusions to Fresh Frozen Plasma and Platelet Transfusion
      2. Preferred over older markers of coagulation (INR, PTT)
3. Mechanism
   1. Whole blood assay of a blood's ability to clot based on viscoelastic blood properties
      1. Provides dynamic coagulation assessment of Platelet function, clot strength, factor concentrates
      2. Plots initial Fibrin development, Fibrin-Platelet aggregation and clot lysis
   2. As blood clot forms, analyzer detects resistance over time
      1. Analyzer plots measurized resistance over time in form of a graph
      2. Typically graph is plotted over a 20-30 minute period until maximal clot firmness
      3. Predicts bleeding and thrombosis risk
      4. Also identifies hyperfibrinolysis
4. Labs: Bedside Viscoelastic Assay
   1. Thromboelastography (TEG)
      1. Reported as reaction time (R)
   2. Rapid Thromboelastography (r-TEG)
      1. Reported as Activated Clotting Time (ACT)
      2. Assay is faster than TEG due to added tissue factor and Kaolin (speeds clotting activation)
      3. Initial results available within 3 minutes (final results in 30 minutes)
      4. Detector wire protrudes into a small sample of blood (350 ul) in oscillating cup at 37 C
   3. Rotational Thromboelastography (ROTEM)
5. Interpretation: General
   1. Abnormal Clotting Time
      1. In early trauma Coagulopathy, often related to plasma related deficiencies
      2. In later trauma Coagulopathy, Fibrinogen deficiency may be treated with Cryoprecipitate or Fibrinogen
   2. Poor maximal clot firmness (poor maximal amplitude)
      1. Consider Platelet Transfusion
   3. Hyperfibrinolysis
      1. Typically assumed as a part of early trauma Coagulopathy, and Tranexamic Acid is given empirically
      2. May appear as abnormal clot breakdown over time (typically subtle in graph)
6. Precautions
   1. Viscoelastic Assays do not measure Platelet inhibition by antiplatelet agents (e.g. Aspirin, Clopidogrel)
7. Interpretation: Rapid Thromboelastography (r-TEG)
   1. Activated Clotting Time (ACT or R-Time)
      1. Normal 0-118 seconds
      2. Represents Clotting Factor acivity and initial Fibrin formation (most important rTEG result in Hemorrhage)
      3. Decreased in Hypercoagulable state
      4. Increased in Clotting Factor deficiency, severe hemodilution (consider FFP)
   2. K-Time
      1. Normal 1-2 min
      2. Represents time to initial clot strength target (measures Fibrin and Platelet interaction)
      3. Prolonged in Fibrinogen or Platelet deficiency (consider Platelet Transfusion)
   3. Alpha angle
      1. Normal 66 to 82 degrees
      2. Represents slope of Clot Formation (Fibrin formation and Platelet-Fibrin interaction)
      3. Low angles (decreased slope) reflects slow Fibrin formation
      4. Decreased in Fibrinogen or Platelet deficiency (consider Platelet Transfusion or Cryoprecipitate)
   4. Maximum Amplitude (mA)
      1. Normal 54 to 72 mm
      2. Represents greatest clot strength and Platelet function
      3. Decreased in Fibrinogen or Platelet deficiency (consider Platelet Transfusion, Cryoprecipitate, DDAVP)
      4. Increased in excess Platelet activity
   5. G-Value
      1. Normal 5.3K to 12.4K dynes/cm2
      2. Overall clot strength measure (used by Paramedics in prehospital setting)
      3. Increased in Hypercoagulable states and decreased in hypocoagulable states
   6. Ly30 (Lysis Time, Estimated Percent Lysis, EPL)
      1. Normal <3 to 7.5% (clinically important at >3%)
      2. Measured amplitude reduction (percent) at 30 minutes following Maximum Amplitude (mA)
      3. Reflects clot stability and firmness
      4. Increased (>3%) in hyperfibrinolysis (consider TXA if <3 hours from time of injury)
      5. Ly30 >3% is an important prognostic indicator in Hemorrhagic Shock
         1. Markedly increased all cause mortality
         2. Cripps (2013) J Trauma Acute Care Surg 75(2 Suppl 2): S255-62 [PubMed]
8. Resources
   1. Shaydakov, Sigmon, Blebea (2019) Stat Pearls
      1. https://www.ncbi.nlm.nih.gov/books/NBK537061/
9. References
   1. Freeman and Bourland (2021) Crit Dec Emerg Med 35(12): 3-11
   2. Swaminathan and Hicks in Herbert (2020) EM:Rap 20(7): 1-2