ECMO Physiology and Principles 4

Question 1

In VA-ECMO, how does left ventricular (LV) afterload change compared to a patient without ECMO support?

Accepted Answer

LV afterload increases because retrograde ECMO flow opposes ventricular ejection

Answer

Retrograde aortic flow from femoral VA-ECMO increases LV afterload, which can worsen LV distension and pulmonary edema in patients with severely impaired LV function.

Question 2

What does the term 'ECMO recirculation' mean, and how is it measured?

Accepted Answer

Re-aspiration of already-oxygenated blood into the drainage cannula; estimated from SvO2 and SaO2 values

Answer

Recirculation is the fraction of oxygenated blood returning from the ECMO circuit that is immediately re-drained before circulating through the patient, estimated using venous and arterial saturation values.

Question 3

Which of the following best explains why pulsatility is important to maintain during VA-ECMO support?

Accepted Answer

Pulsatile flow preserves microvascular function and organ perfusion pressure waveforms

Answer

Pulsatile flow maintains physiologic microvascular tone and endothelial function; prolonged non-pulsatile VA-ECMO flow is associated with end-organ dysfunction.

Question 4

What is the 'pressure-flow' curve concept as it applies to ECMO centrifugal pumps?

Accepted Answer

The relationship between pump speed and resulting flow, which shifts with changes in preload and afterload

Answer

Centrifugal pump pressure-flow curves show that at a given RPM, flow varies with inlet pressure (preload) and outlet resistance (afterload), requiring continuous flow monitoring rather than relying on RPM alone.

Question 5

During ECMO, what is the physiological basis for 'metabolic alkalosis' developing when citrate anticoagulation is used?

Accepted Answer

Citrate is metabolized to bicarbonate in the liver, raising plasma pH

Answer

Citrate is metabolized in the liver to bicarbonate, and in high doses (or with impaired liver function) can cause significant metabolic alkalosis.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Principles 4