Thromboelastography

TEG = thromboelastography

ROTEM = rotational thromboelastometry

Both TEG and ROTEM are methods of measuring coagulation and fibrinolysis.  In TEG, the “cup” of the machine rotates, whereas in ROTEM, it is the sensor shaft that rotates.

In thromboelastography, blood is rotated by 4`45″ 6x per minute to simulate sluggish blood flobe.  A wire probe is then used to measure the speed of coagulation and extent of fibrinolysis.

Thromboelastography measures 4 parameters of blood coagulation (reaction time, K value, alpha angle and maximum amplitude) and 2 parameters of clot lysis (estimated percentage of lysis and percent clot lysed after 30 minutes).  Two other values are calculated based on a proprietary formula from the company who created the machine (coagulation index).

The parameters for clot formation:

1.  Reaction time (R) – time to first clot detected, reflects coagulation factor activity

2.  K value (K) – time from (R) until clot reaches 20mm, reflects speed of clot formation

3.  alpha angle (A) – the tangent of the curve when K is reached, also reflects speed of clot formation; represents thrombin burst and conversion of fibrinogen to fibrin

4.  maximum amplitude (MA) – reflects clot strength; 80% is dervied fro platelet function and 20% from fibrin

The calculated parameters:

1.  COAGULATION INDEX (CI)

2.  G VALUE – log-derivation of MA, also represents clot strenght using dynes/sec as units;  rising levls may be seen in venous thromboembolic disease

The parameters for clot lysis:

1.  Estimated % lysis (EPL)

2.  % clot lysed after 30 minutes (LY30%)


Based on the TEG values, the following treatments may be given:

1.  Elevated R – give plasma

2.  decreased  alpha angle – give cryoprecipitate or large volume of plasma

3.  decreased MA – platelet transfusion or DDAVP

4.  increased EPL or LY30% – treat with antifibrinolytics (i.e. tranexamic acid or aminocaproic acid)
  
  

TEG Procedure:

1. Citrates blood introduced into the sample cup of the TEG machine

2. Cup oscillates around submerged torsion pin which is connected to a computer.

3. As coagulation occurs, pin adheres to clot and begins to move with it.

4. Magnitude of pin motion directly proportional to strength of the clot. Pin motion is displayed graphically by the computer. Torsion pin remains motionless until clotting begins.

5. Amplitude decreases as fibrinolysis begins and the pin begins to slip.

6. Graph analyzed and 5 parameters are measured.

TEG PARAMETERS:

1. R – time elapsed until first measurable clot forms. Impacted by coagulation factors.

2. K – time elapsed until clot reaches a fixed strength (20mm). Impacted by fibrinogen

3. Alpha angle – reflects speed of fibrin accumulation. Impacted by fibrinogen

4. MA – highest vertical amplitude of TEG tracing. Impacted by platelets.

5. LY30 – percentage of amplitude reduction 30 minutes after maximum. Measures fibrinolysis.

Interpretation of TEG:

R normal range is 5-10 minutes. Elevation represents deficient clotting factors and is treated with FFP.

K normal range is 1-3 units. Elevation represents deficient fibrinogen and is treated with cryoprecipitate.

Alpha angle normal is 53-72 degrees. A low value represents deficient fibrinogen and is treated with cryoprecipitate.

MA normal range is 50-70 mm. A low value represents deficient platelets and is treated with platelets.

LY30 normal range is 0-8%. A higher value indicates excess fibrinolysis and is treated with antifibrionlytics s.a. aminocaproic acid.

 

Another study uses the following normal parameters:

  1. R time 22-44 s
  2. k time 34-138s
  3. alpha angle 64-80 degrees
  4. MA 55-71mm
  5. LY30 0%

 

References:

Martin, G., Shah, D., Elson, N., Boudreau, R., Hanseman, D., Pritts, T., Makley, A., Foreman, B. and Goodman, M. (2018). Relationship of Coagulopathy and Platelet Dysfunction to Transfusion Needs After Traumatic Brain Injury. Neurocritical Care.

YouTube. (2018). Thromboelastography. [online] Available at: https://www.youtube.com/watch?v=SjH05uGSGv0 [Accessed 2 Apr. 2018].

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