ECMO Veno-Venous (VV) ECMO Management 5 — Questions and Answers
Question 1: Which condition would most likely prompt conversion from VV to VA ECMO in a patient already on VV support?
- Worsening hypoxemia despite optimal ECMO settings
- Progressive cardiogenic shock with hemodynamic deterioration (Correct answer)
- Development of ventilator-associated pneumonia
- Rising serum lactate due to sepsis without cardiac dysfunction
Correct answer: Progressive cardiogenic shock with hemodynamic deterioration
VV ECMO provides only respiratory support; progressive cardiogenic shock requiring hemodynamic support necessitates conversion to VA ECMO, which also offloads the failing heart.
Question 2: A VV ECMO patient's sweep gas accidentally becomes disconnected for 3 minutes. What is the expected physiologic consequence?
- Rapid hypoxemia and hypercapnia (Correct answer)
- Hypoxemia only with compensatory respiratory alkalosis
- Hypercapnia only with maintained oxygenation
- No significant change if native lung function is partial
Correct answer: Rapid hypoxemia and hypercapnia
Loss of sweep gas eliminates both O2 transfer and CO2 removal across the membrane, causing rapid hypoxemia and hypercapnia.
Question 3: During VV ECMO, thrombocytopenia and prolonged aPTT develop simultaneously. Anti-PF4 antibody is strongly positive. What is the recommended treatment?
- Increase unfractionated heparin dose
- Stop heparin and switch to a direct thrombin inhibitor (bivalirudin or argatroban) (Correct answer)
- Administer IVIG and continue heparin at reduced dose
- Transfuse platelets and continue current anticoagulation
Correct answer: Stop heparin and switch to a direct thrombin inhibitor (bivalirudin or argatroban)
Positive anti-PF4 antibody confirms heparin-induced thrombocytopenia; heparin must be stopped and replaced with a non-heparin anticoagulant such as bivalirudin.
Question 4: What is the significance of a 'chattering' or 'sucking' cannula during VV ECMO?
- It indicates optimal flow with maximal oxygenation efficiency
- It signals that drainage is impaired, usually from hypovolemia or cannula malposition (Correct answer)
- It is caused by excessive anticoagulation causing blood thinning
- It reflects normal pulsatile flow from cardiac contractions
Correct answer: It signals that drainage is impaired, usually from hypovolemia or cannula malposition
Cannula chattering occurs when the circuit intermittently collapses venous inflow, indicating inadequate preload or a positional drainage issue requiring immediate attention.
Question 5: A VV ECMO patient with ARDS is being weaned. During a 4-hour trial with sweep gas at 0 L/min, PaO2 is 72 mmHg on FiO2 0.4. Ventilator settings are Vt 6 mL/kg, PEEP 10 cmH2O, RR 20. What is the appropriate next step?
- Immediately decannulate the patient (Correct answer)
- Extend the trial to 24 hours before deciding on decannulation
- Restore sweep gas — trial criteria not met
- Increase PEEP to 14 cmH2O and repeat trial
Correct answer: Immediately decannulate the patient
PaO2 >65 mmHg on FiO2 ≤0.4 and acceptable ventilator parameters during a sweep-off trial indicate adequate native lung recovery and readiness for decannulation.
Question 6: Which physiologic difference distinguishes VV from VA ECMO regarding oxygen delivery to the coronary arteries?
- In VV ECMO, oxygenated blood returns directly to the aorta, ensuring coronary perfusion with fully oxygenated blood
- In VV ECMO, oxygenated blood mixes with desaturated blood in the right heart and must traverse the native cardiopulmonary circulation before reaching coronary arteries (Correct answer)
- In VA ECMO, all coronary perfusion depends entirely on the native lungs
- In VV ECMO, coronary arteries are bypassed by the ECMO circuit
Correct answer: In VV ECMO, oxygenated blood mixes with desaturated blood in the right heart and must traverse the native cardiopulmonary circulation before reaching coronary arteries
In VV ECMO, oxygenated blood returned to the right atrium mixes with desaturated blood and must pass through the native lungs before reaching the left heart and coronary circulation.
Question 7: Which parameter should be checked when a VV ECMO patient receiving therapeutic anticoagulation unexpectedly develops widespread circuit clotting?
- Factor V Leiden mutation status
- Antithrombin III (AT-III) level (Correct answer)
- Protein C and S levels
- D-dimer concentration
Correct answer: Antithrombin III (AT-III) level
Heparin requires antithrombin III to exert its anticoagulant effect; AT-III deficiency causes heparin resistance and circuit thrombosis despite therapeutic dosing.
ECMO Veno-Venous (VV) ECMO Management 5
Which condition would most likely prompt conversion from VV to VA ECMO in a patient already on VV support?