ECMO Circuit Components and Management 5 — Questions and Answers
Question 1: During ECMO circuit change-out, the most critical step to prevent air embolism is:
- Ensuring all tubing connections are primed and bubble-free before unclamping (Correct answer)
- Administering a heparin bolus 30 minutes before the procedure
- Reducing pump speed to minimum RPM throughout the exchange
- Converting from VV to VA configuration temporarily
Correct answer: Ensuring all tubing connections are primed and bubble-free before unclamping
Any air introduced during circuit change-out can cause fatal embolism, so meticulous priming and de-airing of all new components is mandatory before reconnecting to the patient.
Question 2: Hemolysis in an ECMO circuit is best monitored by measuring:
- Plasma-free hemoglobin and lactate dehydrogenase (LDH) levels (Correct answer)
- Serum potassium and sodium levels
- Activated clotting time and anti-Xa levels
- Post-membrane PO2 and PCO2
Correct answer: Plasma-free hemoglobin and lactate dehydrogenase (LDH) levels
Plasma-free hemoglobin and LDH are direct markers of red cell destruction, indicating mechanical trauma from pump cavitation, high negative pressures, or circuit thrombosis.
Question 3: Inlet pressure (P-in) monitoring on the venous drainage limb of ECMO is important because extreme negative pressures can cause:
- Hemolysis, cavitation, and venous collapse around the cannula tip (Correct answer)
- Arterial hypertension and increased cardiac afterload
- Oxygenator plasma leakage
- Hyperthermia from increased pump work
Correct answer: Hemolysis, cavitation, and venous collapse around the cannula tip
Excessive negative suction pressures on the venous drainage side cause red cell destruction, gas bubble formation (cavitation), and vessel wall collapse at the cannula.
Question 4: Which anticoagulant is used as an alternative to heparin in patients with heparin-induced thrombocytopenia (HIT) on ECMO?
- Bivalirudin (a direct thrombin inhibitor) (Correct answer)
- Warfarin (a vitamin K antagonist)
- Clopidogrel (a P2Y12 inhibitor)
- Fondaparinux (a factor Xa inhibitor)
Correct answer: Bivalirudin (a direct thrombin inhibitor)
Bivalirudin is the preferred anticoagulant alternative for ECMO patients with HIT because it directly inhibits thrombin and has a short half-life allowing rapid titration.
Question 5: The ECMO specialist notes that the post-membrane PO2 has dropped from 450 to 180 mmHg despite unchanged sweep gas settings. The most likely explanation is:
- Oxygenator clotting reducing functional membrane surface area (Correct answer)
- Patient's native lung function has improved
- Pump speed has inadvertently increased
- Arterial cannula has migrated into the left ventricle
Correct answer: Oxygenator clotting reducing functional membrane surface area
Clot accumulation within the fiber bundle reduces available gas exchange surface, causing a fall in post-oxygenator PO2 even with maintained sweep gas flow.
Question 6: When weaning VV-ECMO, which parameter best indicates readiness for decannulation?
- Adequate arterial oxygenation and ventilation maintained at low-to-moderate ventilator settings with ECMO flow reduced to 1–2 L/min and sweep gas near zero (Correct answer)
- Normalization of serum lactate alone
- Recovery of native cardiac output on echocardiography
- Absence of arrhythmias for 24 consecutive hours
Correct answer: Adequate arterial oxygenation and ventilation maintained at low-to-moderate ventilator settings with ECMO flow reduced to 1–2 L/min and sweep gas near zero
Successful VV-ECMO wean requires that native lungs sustain acceptable gas exchange on acceptable ventilator settings as ECMO flow and sweep gas are progressively reduced.
Question 7: What is the purpose of the 'bridge' (or bypass loop) incorporated into some ECMO circuits?
- To allow the circuit to continue circulating during emergent oxygenator or pump head exchange without interrupting perfusion (Correct answer)
- To measure recirculation fraction in VV-ECMO
- To deliver medications directly into the oxygenator gas phase
- To monitor transmembrane pressure gradient continuously
Correct answer: To allow the circuit to continue circulating during emergent oxygenator or pump head exchange without interrupting perfusion
A bridge loop connects the arterial and venous limbs, allowing the circuit to be recirculated while a failed component is changed out without exposing the patient to air or prolonged ischemia.
ECMO Circuit Components and Management 5
During ECMO circuit change-out, the most critical step to prevent air embolism is: