ECMO Anticoagulation and Hemostasis 4 — Questions and Answers
Question 1: Which ECMO configuration carries the highest risk of arterial thromboembolism due to retrograde aortic blood flow interactions?
- VV-ECMO with right internal jugular cannulation
- VA-ECMO with femoral artery return cannula (Correct answer)
- VV-ECMO with bicaval dual-lumen cannula
- VAV-ECMO configuration
Correct answer: VA-ECMO with femoral artery return cannula
Femoral VA-ECMO creates a watershed zone where oxygenated retrograde ECMO flow meets anterograde native cardiac output, increasing thrombus and watershed infarction risk.
Question 2: In a patient on ECMO with suspected HIT, a 4T score of 6 is calculated. What is the appropriate next step?
- Continue heparin and recheck platelet count in 24 hours
- Stop heparin immediately and start a direct thrombin inhibitor while confirmatory testing is sent (Correct answer)
- Reduce heparin dose by 50%
- Switch to low-molecular-weight heparin
Correct answer: Stop heparin immediately and start a direct thrombin inhibitor while confirmatory testing is sent
A 4T score of 6 represents high probability of HIT; heparin must be stopped immediately and an alternative anticoagulant started while awaiting confirmatory anti-PF4 antibody results.
Question 3: What is the primary reason aPTT is considered an inferior monitoring tool compared to anti-Xa for heparin dosing in ECMO?
- aPTT cannot detect heparin levels above 0.3 IU/mL
- aPTT is affected by many non-heparin variables including factor deficiencies and acute phase reactants (Correct answer)
- aPTT requires arterial blood sampling
- Anti-Xa testing is faster and cheaper
Correct answer: aPTT is affected by many non-heparin variables including factor deficiencies and acute phase reactants
aPTT is influenced by multiple variables common in ECMO patients — factor consumption, lupus anticoagulant, elevated factor VIII — making it an unreliable surrogate for heparin effect.
Question 4: A patient on VV-ECMO for ARDS requires urgent surgical tracheostomy. How should anticoagulation be managed perioperatively?
- Continue heparin unchanged throughout the procedure
- Hold heparin 4–6 hours before and restart 2–4 hours post-procedure (Correct answer)
- Reverse heparin with protamine before incision
- Switch to oral anticoagulation 12 hours before the procedure
Correct answer: Hold heparin 4–6 hours before and restart 2–4 hours post-procedure
For surgical procedures on ECMO, heparin is typically held 4–6 hours pre-procedure and restarted 2–4 hours post-procedure once hemostasis is achieved, balancing thrombotic and bleeding risk.
Question 5: What is the clinical significance of detecting a rising D-dimer trend in an ECMO patient whose ACT is therapeutic?
- It confirms adequate fibrinolysis and circuit patency
- It may indicate developing circuit thrombosis or DIC requiring circuit inspection (Correct answer)
- It reflects normal heparin metabolism
- It indicates heparin overdose
Correct answer: It may indicate developing circuit thrombosis or DIC requiring circuit inspection
Rising D-dimer despite therapeutic ACT suggests active thrombus formation and fibrinolysis within the circuit or patient vasculature, warranting urgent circuit inspection.
Question 6: Which pharmacokinetic property of bivalirudin makes it advantageous over argatroban in patients with hepatic failure on ECMO?
- Bivalirudin is renally cleared and not hepatically metabolized
- Bivalirudin is primarily metabolized by enzymatic cleavage in plasma, independent of liver function (Correct answer)
- Bivalirudin has a longer half-life, allowing less frequent dosing
- Bivalirudin is protein-bound, reducing free drug accumulation
Correct answer: Bivalirudin is primarily metabolized by enzymatic cleavage in plasma, independent of liver function
Bivalirudin is metabolized primarily by thrombin-mediated proteolysis and non-specific plasma proteases, not by hepatic enzymes, making it predictable in liver failure.
Question 7: During ECMO decannulation, protamine is administered to reverse heparin. What is the most feared complication of protamine administration?
- Rebound anticoagulation 4–6 hours later
- Severe pulmonary hypertension and cardiovascular collapse (Correct answer)
- Prolonged thrombocytopenia lasting weeks
- Acute kidney injury from protein precipitation
Correct answer: Severe pulmonary hypertension and cardiovascular collapse
Protamine can trigger complement activation, thromboxane release, and pulmonary vasoconstriction, causing acute severe pulmonary hypertension and cardiovascular collapse, especially in right-heart-failure patients.
ECMO Anticoagulation and Hemostasis 4
Which ECMO configuration carries the highest risk of arterial thromboembolism due to retrograde aortic blood flow interactions?