ECMO Physiology and Pathophysiology 3

Question 1

A patient on VV-ECMO develops worsening hypercapnia despite maximal sweep gas flow. What is the most likely explanation?

Accepted Answer

Oxygenator thrombosis reducing effective membrane surface area

Answer

Oxygenator thrombosis progressively reduces functional membrane surface area, impairing both oxygen transfer and CO2 elimination despite maximal sweep gas flows.

Question 2

What is the physiological rationale for maintaining a target ACT of 160-200 seconds during ECMO rather than full anticoagulation (ACT >400)?

Accepted Answer

Balancing thrombosis prevention against hemorrhagic complications given the procoagulant surface of the circuit

Answer

The ECMO circuit's artificial surfaces activate coagulation, but excessive anticoagulation dramatically increases bleeding risk, so moderate heparin targets balance clot prevention with hemorrhage avoidance.

Question 3

How does ECMO-induced hemolysis contribute to renal injury?

Accepted Answer

Free hemoglobin causes renal tubular toxicity and vasoconstriction of the renal microvasculature

Answer

Free plasma hemoglobin released during hemolysis is directly nephrotoxic, causing oxidative tubular injury and scavenging nitric oxide to produce renal vasoconstriction and ischemia.

Question 4

In ARDS patients on VV-ECMO, why is ultra-protective ventilation (TV 2-4 mL/kg) physiologically preferable?

Accepted Answer

It minimizes ventilator-induced lung injury while ECMO maintains gas exchange, allowing lung rest

Answer

VV-ECMO assumes the gas exchange burden, permitting extremely low tidal volumes that minimize cyclic alveolar stretch, barotrauma, and biotrauma, facilitating lung recovery.

Question 5

What hemodynamic consequence occurs when ECMO flow is abruptly reduced in a patient with severe cardiogenic shock on VA-ECMO?

Accepted Answer

Precipitous drop in mean arterial pressure and end-organ perfusion

Answer

In cardiogenic shock, systemic perfusion depends on ECMO flow; abrupt reduction removes the primary driver of cardiac output and tissue oxygen delivery, causing immediate hemodynamic collapse.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Physiology and Pathophysiology 3