ECMO Foundations of ECMO and ECMO Management 5 — Questions and Answers
Question 1: The pre-pump (inlet) pressure on an ECMO circuit is characteristically:
- Positive, reflecting aortic backpressure
- Negative, reflecting the suction generated by the drainage cannula (Correct answer)
- Equal to central venous pressure
- Atmospheric (zero) during normal operation
Correct answer: Negative, reflecting the suction generated by the drainage cannula
The inlet (drainage) limb operates at subatmospheric (negative) pressure as the pump generates suction to pull blood from the venous circulation.
Question 2: An ECMO patient develops sudden circuit thrombosis with loss of flow. The immediate priority is:
- Administer protamine to reverse heparin
- Clamp cannulas, initiate CPR if indicated, and prepare for emergency circuit change (Correct answer)
- Increase pump RPM to force flow through the clot
- Start thrombolytics via the circuit
Correct answer: Clamp cannulas, initiate CPR if indicated, and prepare for emergency circuit change
Cannula clamping prevents air or emboli from entering the patient, CPR maintains perfusion if needed, and a circuit change is performed urgently to restore ECMO support.
Question 3: When weaning VV-ECMO, the clinician assesses readiness by:
- Measuring cardiac output with a pulmonary artery catheter
- Reducing sweep gas flow to zero and observing native gas exchange on the ventilator (Correct answer)
- Clamping the venous cannula and monitoring SvO2
- Removing the oxygenator from the circuit while maintaining pump flow
Correct answer: Reducing sweep gas flow to zero and observing native gas exchange on the ventilator
A VV-ECMO weaning trial involves turning sweep gas to zero so the oxygenator is bypassed functionally, allowing assessment of whether the native lungs can sustain adequate gas exchange.
Question 4: A patient on VA-ECMO for cardiogenic shock shows improving echo function. The correct weaning strategy involves:
- Abruptly stopping ECMO and observing hemodynamics
- Gradually reducing ECMO flow while monitoring hemodynamic parameters and echo (Correct answer)
- Increasing vasopressor doses before reducing ECMO flow
- Transitioning to VV-ECMO before decannulation
Correct answer: Gradually reducing ECMO flow while monitoring hemodynamic parameters and echo
VA-ECMO is weaned by stepwise flow reductions with concurrent hemodynamic and echocardiographic monitoring to confirm the heart can sustain adequate output.
Question 5: Which laboratory finding during ECMO warrants the most urgent evaluation for heparin-induced thrombocytopenia (HIT)?
- Platelet count drop from 180,000 to 140,000 over 7 days
- Platelet count drop of greater than 50% on days 5–10 despite no circuit changes (Correct answer)
- Mild elevation in ACT to 230 seconds
- Elevated plasma-free hemoglobin
Correct answer: Platelet count drop of greater than 50% on days 5–10 despite no circuit changes
A >50% platelet count drop on days 5–10 of heparin exposure is the classic temporal pattern raising strong suspicion for HIT, warranting a 4T score assessment and HIT antibody testing.
Question 6: The term 'ECMO-CPR' (ECPR) refers to:
- Using ECMO flow to generate chest compressions mechanically
- Initiating VA-ECMO during active cardiac arrest to restore perfusion (Correct answer)
- Using ECMO oxygenation to support prolonged CPR in neonates only
- Administering ACLS drugs directly into the ECMO circuit during arrest
Correct answer: Initiating VA-ECMO during active cardiac arrest to restore perfusion
ECPR is the deployment of VA-ECMO during refractory cardiac arrest to restore systemic perfusion and allow time for resuscitation, intervention, or recovery.
Question 7: Which statement about the ECMO oxygenator membrane is correct?
- It allows direct blood-gas contact for maximum efficiency
- Modern hollow-fiber membranes use microporous or diffusion-based fibers to transfer gases without plasma leak (Correct answer)
- Silicone sheet membranes are standard in all current adult ECMO devices
- The membrane primarily removes CO2 and is ineffective at oxygenation
Correct answer: Modern hollow-fiber membranes use microporous or diffusion-based fibers to transfer gases without plasma leak
Contemporary hollow-fiber oxygenators use polymethylpentene (PMP) or similar fibers that permit gas diffusion while preventing plasma from leaking into the gas phase.
ECMO Foundations of ECMO and ECMO Management 5
The pre-pump (inlet) pressure on an ECMO circuit is characteristically: