How to correct a prolonged R time in Thromboelastography (TEG)?

Correcting Prolonged R Time in Thromboelastography (TEG)

To correct a prolonged R time in TEG, administer fresh frozen plasma (FFP) or prothrombin complex concentrate (PCC), with fibrinogen concentrate if needed, guided by the specific cause of the prolongation. 1, 2

Understanding R Time and Its Significance

• R time (Reaction time) measures the time to initial fibrin formation, representing the clot initiation phase of coagulation 2
• Prolonged R time indicates coagulation factor deficiency or anticoagulant effect 2
• Normal R time varies by device but is typically 5-10 minutes; values above this suggest hypocoagulability 2
• R time correlates strongly with conventional coagulation tests like PT, INR, and aPTT (r >0.70) 3

Common Causes of Prolonged R Time

• Coagulation factor deficiencies, particularly of the extrinsic and common pathways 2
• Anticoagulant medications, especially:
  • Vitamin K antagonists (warfarin) 1
  • Direct oral anticoagulants (DOACs), particularly dabigatran 1, 4
• Hemodilution from massive fluid resuscitation or transfusion 5
• Liver disease with impaired synthesis of coagulation factors 1
• Hypofibrinogenemia (fibrinogen <2.0 g/L) 6

Treatment Algorithm Based on Cause

1. For Anticoagulant-Related Prolongation:

• For Vitamin K Antagonists (VKAs):

  • Administer PCC along with intravenous vitamin K for urgent correction 1
  • Dosing should be guided by INR level 1
  • For non-urgent cases, vitamin K alone may be sufficient (takes 6-12 hours for effect) 1

• For Dabigatran:

  • Administer idarucizumab (Praxbind) for immediate reversal 4
  • TEG can be used to monitor reversal effectiveness 1

• For Factor Xa Inhibitors:

  • Administer andexanet alfa or PCC 1
  • Monitor effectiveness with anti-Xa assays rather than TEG alone 1

2. For Hypofibrinogenemia:

• Administer fibrinogen concentrate or cryoprecipitate if fibrinogen levels are <2.0 g/L 6
• Fibrinogen concentrate dose of 4g can effectively increase fibrinogen levels by approximately 0.9 g/L 6
• Target fibrinogen level >2.0-2.5 g/L to normalize TEG parameters 6

3. For Dilutional Coagulopathy:

• Administer FFP (10-15 mL/kg) as first-line treatment 1, 5
• Consider fibrinogen concentrate (4g/70kg) if significant hemodilution (>50%) is present 5
• For massive transfusion scenarios, maintain 1:1:1 ratio of packed RBCs, FFP, and platelets 1

Monitoring Treatment Effectiveness

• Repeat TEG 15-30 minutes after intervention to assess response 1
• Target R time normalization (typically <8 minutes, but use device-specific reference ranges) 2
• An R time threshold of 3.9-4.3 minutes provides optimal sensitivity and specificity for detecting factor deficiencies 7
• Consider that current ACS guidelines for FFP transfusion based on R time are highly specific but have low sensitivity (3-7%) 7

Important Caveats and Pitfalls

• Standard TEG is insensitive to antiplatelet agents and cannot reliably detect platelet dysfunction 2
• TEG shows high coefficients of variance (7.1-39.9% for TEG parameters), requiring careful interpretation 2
• Results vary between devices (TEG vs. ROTEM) and are not interchangeable 2
• Anemia can paradoxically show hypercoagulable TEG results due to decreased blood viscosity 2
• When using TEG to monitor anticoagulant effects, a difference >25% between plain and heparinase R time samples indicates significant anticoagulant effect 1
• In trauma settings, an ACT >128 seconds (equivalent to prolonged R time) predicts need for massive transfusion 3, 8

Special Considerations

• In pregnancy, baseline R times are typically shortened due to physiologic hypercoagulability 1
• In liver disease, viscoelastic tests may guide more targeted blood product use with fewer transfusions 1
• In trauma patients, goal-directed therapy using TEG parameters has been shown to improve survival and reduce blood product waste compared to conventional coagulation test-guided therapy 1