ECMO Physiology and Principles 3

Question 1

What is the primary mechanism by which ECMO causes hemolysis?

Accepted Answer

Shear stress from the centrifugal or roller pump mechanism

Answer

Mechanical shear stress generated by the ECMO pump (particularly at high flows or with small tubing) is the primary cause of red blood cell destruction during ECMO.

Question 2

During ECMO, why is the SvO2 (mixed venous oxygen saturation) measured in the drainage limb clinically important?

Accepted Answer

It indicates adequacy of oxygen delivery relative to consumption

Answer

Low drainage-limb SvO2 indicates that tissues are extracting more oxygen than is being delivered, signaling inadequate ECMO support or increased metabolic demand.

Question 3

What happens to PaCO2 when sweep gas flow is doubled while ECMO blood flow remains constant?

Accepted Answer

PaCO2 decreases, potentially causing hypocapnia

Answer

Doubling sweep gas flow dramatically increases CO2 removal, often causing significant hypocapnia, so sweep adjustments require careful monitoring of blood gas values.

Question 4

In a centrifugal ECMO pump, what is the effect of an acute increase in afterload (e.g., arterial hypertension) on pump flow?

Accepted Answer

Flow decreases as the pump is sensitive to pressure changes

Answer

Unlike roller pumps, centrifugal pumps are not occlusive and their flow decreases when afterload increases, making continuous flow monitoring essential.

Question 5

What is the physiological rationale for targeting a lower 'lung-protective' ventilator strategy (ultra-protective ventilation) during VV-ECMO?

Accepted Answer

ECMO assumes gas exchange, allowing the lungs to rest and potentially recover from VILI

Answer

With ECMO handling gas exchange, tidal volumes and pressures can be minimized to prevent ventilator-induced lung injury (VILI) and promote lung recovery.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Principles 3