ECMO - Extracorporeal Membrane Oxygenation ECMO Physiology and Principles Questions and Answers

Question 1

In a patient on Veno-Venous (VV) ECMO for severe ARDS, the primary determinant of carbon dioxide removal (decarboxylation) is the:

Accepted Answer

Sweep gas flow rate (L/min)

Answer

Carbon dioxide removal in the ECMO circuit is primarily dependent on the sweep gas flow rate. The fresh gas (sweep gas) flowing through the oxygenator creates a concentration gradient that drives CO2 out of the blood. While blood flow and membrane surface area play a role, the sweep gas flow is the most direct and primary control for adjusting PaCO2.

Question 2

A patient is on peripheral Veno-Arterial (VA) ECMO via the femoral vessels for cardiogenic shock. The patient begins to show signs of myocardial recovery, and the team notes that the SpO2 on the right hand is consistently lower than the SpO2 on the foot. This phenomenon is best described as:

Accepted Answer

Harlequin Syndrome (Differential Hypoxia)

Answer

This scenario describes Harlequin Syndrome, or differential hypoxia. It occurs in peripheral VA ECMO when the patient's heart recovers and begins to eject poorly oxygenated blood from the native lungs, which preferentially perfuses the upper body (including the heart and brain). The well-oxygenated blood from the ECMO circuit flows retrograde up the aorta but may not reach the aortic arch, leading to lower oxygen saturation in the upper extremities compared to the lower extremities.

Question 3

Which of the following physiological changes is an expected effect of initiating Veno-Arterial (VA) ECMO in a patient with profound cardiogenic shock?

Accepted Answer

Increased left ventricular afterload

Answer

Initiating VA ECMO involves returning oxygenated blood into the arterial system under pressure. This retrograde flow opposes the native cardiac ejection, thereby increasing the afterload that the left ventricle must pump against. While VA ECMO decreases preload by draining venous blood, it characteristically increases LV afterload, which can be detrimental if not managed properly.

Question 4

A patient on Veno-Venous (VV) ECMO for respiratory failure develops worsening hypoxemia despite a high FdO2 of 1.0. The pre-oxygenator saturation (venous blood entering the circuit) is noted to be rising, and the post-oxygenator saturation remains high. Which of the following is the most likely cause?

Accepted Answer

Significant recirculation

Answer

Recirculation occurs in VV ECMO when a significant fraction of the newly oxygenated blood returned to the patient is immediately drained back into the ECMO circuit without circulating systemically. This is often due to the proximity of the drainage and return cannulas. A key sign is a rising pre-oxygenator saturation, as the circuit is draining already oxygenated blood, which reduces the efficiency of systemic oxygen delivery and causes patient hypoxemia.

Question 5

In managing a patient on VV ECMO, increasing the ECMO blood flow rate (Qb) will have the most direct and significant impact on which of the following parameters?

Accepted Answer

Patient's arterial oxygenation (PaO2)

Answer

In VV ECMO, the patient's arterial oxygenation is primarily determined by the amount of oxygenated blood delivered by the circuit relative to the patient's total cardiac output. Increasing the ECMO blood flow rate (Qb) increases the delivery of oxygen (DO2) from the circuit, which has the most direct and significant impact on improving the patient's PaO2 and SaO2. While flow can influence recirculation, its primary therapeutic target is oxygenation.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation ECMO Physiology and Principles Questions and Answers