ECMO Physiology and Pathophysiology 5

Question 1

What physiological parameter best guides ECMO flow titration to ensure adequate oxygen delivery (DO2) in VA-ECMO?

Accepted Answer

Mixed venous oxygen saturation (SvO2) reflecting the balance between DO2 and VO2

Answer

SvO2 integrates oxygen delivery and consumption; a falling SvO2 indicates tissues are extracting more oxygen to compensate for inadequate delivery, signaling the need to increase ECMO flow or hemoglobin.

Question 2

In neonatal ECMO for persistent pulmonary hypertension of the newborn (PPHN), what is the primary pathophysiological target?

Accepted Answer

Reducing pulmonary vascular resistance to enable transition from fetal to neonatal circulation

Answer

PPHN results from failure of the pulmonary vasculature to dilate at birth, maintaining high PVR that drives right-to-left shunting; ECMO buys time while strategies to reduce PVR (inhaled NO, alkalosis, oxygen) take effect.

Question 3

How does increasing ECMO blood flow affect plasma-free hemoglobin levels?

Accepted Answer

Hemolysis increases with higher rpm as centrifugal pump shear stress rises proportionally

Answer

Centrifugal pump rpm and shear forces increase with flow; higher shear stress exceeds red cell membrane tolerance, causing progressive mechanical hemolysis that correlates with pump speed.

Question 4

What is the physiological consequence of excessive negative inlet pressure (high suction) at the venous drainage cannula during ECMO?

Accepted Answer

Cavitation, hemolysis, and intermittent flow interruption as the right atrium collapses around the cannula

Answer

Excessive negative pressure causes the compliant right atrial wall to intermittently collapse over the drainage cannula (chatter), inducing cavitation, red cell destruction, and unstable pump flow.

Question 5

Which mechanism best explains why patients with severe right heart failure on VA-ECMO may paradoxically develop pulmonary edema?

Accepted Answer

Improved RV unloading by ECMO increases pulmonary blood flow into the failing LV, which cannot accommodate the increased preload

Answer

When VA-ECMO decompresses the RV and restores pulmonary blood flow, a severely impaired LV that cannot empty adequately develops rising LVEDP transmitted back to the pulmonary capillaries, causing hydrostatic edema.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Pathophysiology 5