Question 8

Created on Thu, 12/17/2015 - 06:28
Last updated on Fri, 04/28/2017 - 19:37
Pass rate: 69%
Highest mark: 9.3

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With respect to thromboelastography and haemostasis:

The image depicted in Figure 1 represents a normal thromboelastogram.

With reference to the parameters labelled in Figure 1:

i.    CT (or R)

ii.    CFT (or K)

iii.    Alpha angle
iv.    MCF (or MA)

v.    LI30 (or LY30 or CL)

a)    Explain what each parameter represents and what it measures.    (60% marks)

Review the following thromboelastograms labelled A – E.

Diagram A represents a normal coagulation profile.

b)    Describe the coagulation status indicated by diagrams B – E.    (40% marks)

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College Answer

a)

R (reaction time or clotting time) is the time elapsed until first measurable clot forms (amplitude of 2mm) and indicates the initiation of haemostasis and is dependent on presence of clotting factors.

K (kinetics or clot formation time) is the time taken to achieve a certain level of clot firmness (amplitude of 20mm) and indicates amplification of the clotting process. Dependent on fibrinogen.

Alpha angle reflects the speed of fibrin accumulation. Dependent on fibrinogen.

MA/MCF is the maximum amplitude or maximum clot firmness and is the highest vertical amplitude of the TEG tracing. Dependent on platelets and fibrin.

LY30 /CL (clot lysis) is the percentage of amplitude reduction 30 min after maximum amplitude and is a measure of fibrinolysis.

b)

B – Anticoagulant therapy or factor deficiency

C – Platelet dysfunction or thrombocytopaenia or fibrinogen deficiency

D – Fibrinolysis e.g. use of t-PA

E – Hypercoagulable state

Discussion

In short form:

  • R (CT) =  clotting factors
  • K =  fibrinogen
  • α-angle =  fibrinogen.
  • MA/MCF = platelets and fibrinogen.
  • LY30 /CL = fibrinolysis.

With detail:

CT and R values:

  • The TEG uses "R" and ROTEM uses "CT" to describe the time it takes for the amplitude to start climbing.  Arbitrarily, the 2mm point is used as a marker that the clotting cascade has started. Causes of a raised CT include any deficiency of clotting factors, or defect in clotting factor function:
    • Anything that causes a raised PT and APTT:
      • Deficiency of clotting factors
      • Heparin (very sensitive - prolonged by 0.15 units per ml of blood, or a systemic heparin dose of less than 750 units for a 70kg adult)
      • Warfarin
    • Direct thrombin inhibitors

CFT and R values:

  • These values describe the time from clot initiation (2mm) to 20mm. They also relate to the activity of the clotting factors, but also incorporates a measure of the effectiveness of fibrin polymerisation, platelet activity and Factor XIII activity.
    • Causes of prolonged CFT
      • Thrombocytopenia
      • Platelet dysfunction
      • Low fibrinogen
      • Severe deficiency of other factors
    • Causes of Shortened CFT
      • Hypercoaguable states

The α-angle:

  • This is different between the machines. TEG uses the slope of a line connecting the point at which the R interval ends and the point at which the K interval ends. ROTEM, in contrast, uses the slope of the line at the 2mm amplitude mark. is the slope of the line connecting the end of the R interval with the end of the K interval. In either case, the slope is determined by the rate of reaction between platelets, fibrin and the clotting cascade factors. It is therefore probably a nonspecific variable. However, the manufacturer of the device insists that fibrinogen activity plays the greatest role in determining the α-angle.
    • Causes of a decreased α-angle
      • Low fibrinogen
      • Poor fibrinogen polymerisation
      • Thrombocytopenia, or platelet dysfunction

Maximum clot firmness (MCF) and maximum amplitude (MA):

  • This variable is primarily a measure of platelet count, platelet function and fibrinogen concentration. There is a strong linear correlation between the log platelet count and MA.

LY30 and CL (or CLT)

  • The TEG  defines the term CLT as 2mm from MA, i.e. the time it takes for the clot to soften enough for the amplitude to decrease by 2mm from its maximum. The ROTEM term LOT (Lysis Onset Time) refers to the time it takes for the amplitude to drop by a 15% difference from the MCF, which is a slightly different parameter. The ROTEM term LY30 refers to the amplitude after 30 minutes has passed, and is another measure of fibrinolysis.
    • Causes of a raised LY30 or CLT include
      • Hyperfibrinolysis
      • Administration of thrombolytic drugs

As for the examples:

A is a normal-looking TEG

B has an extremely prolonged CT, but a normal α-angle and a reasonably normal MCF. One might surmise that either something is missing among the clotting factors, or there is some inhibitor present. The platelet count and fibrinogen levels are probably near normal. One might find such a picture in a patient on warfarin, heparin, or receiving a direct thrombin inhibitor.

C is a TEG of a patient who has plenty of clotting factors; the reaction starts quickly.  The MCF is inadequate, suggesting that platelet dysfunction (or thrombocytopenia) are to blame. The college mention that there may also be a problem with the fibrinogen level, but the good α-angle would suggest otherwise.

D is a TEG of a patient with hyperfirbrinolysis from whatever cause.

E is a patient with a hypercoagulable state; the blood clots quickly, with a very firm clot generated in no time.

References

The LITFL page for TEG is ideal to answer this question: they have lovely TEG silhouettes available for the "important patterns".

Practical haemostasis - page on TEG and ROTEM

Sankarankutty, Ajith, et al. "TEG® and ROTEM® in trauma: similar test but different results." World J Emerg Surg 7.Suppl 1 (2012): S3.

Coakley, Margaret, et al. "Transfusion triggers in orthotopic liver transplantation: a comparison of the thromboelastometry analyzer, the thromboelastogram, and conventional coagulation tests." Journal of cardiothoracic and vascular anesthesia 20.4 (2006): 548-553.

Venema, Lieneke F., et al. "An assessment of clinical interchangeability of TEG® and ROTEM® thromboelastographic variables in cardiac surgical patients." Anesthesia & Analgesia 111.2 (2010): 339-344.

Nielsen, Vance G. "A comparison of the Thrombelastograph and the ROTEM." Blood Coagulation & Fibrinolysis 18.3 (2007): 247-252.

Wikkelsoe, A. J., et al. "Monitoring patients at risk of massive transfusion with Thrombelastography or Thromboelastometry: a systematic review." Acta Anaesthesiologica Scandinavica 55.10 (2011): 1174-1189.