ECMO Circuit Components and Management 3

Question 1

What is the function of the bladder (reservoir) in a gravity-siphon ECMO circuit?

Accepted Answer

To buffer venous return and trigger servo-regulation if flow drops

Answer

The venous bladder acts as a reservoir that collapses when venous return is inadequate, triggering servo-regulation to reduce pump speed and prevent suction injury.

Question 2

Polymethylpentene (PMP) hollow fiber oxygenators have largely replaced silicone membrane oxygenators in ECMO because PMP offers:

Accepted Answer

Lower resistance to blood flow and reduced plasma leakage

Answer

PMP fibers are true diffusion membranes that minimize plasma leakage (weeping) while providing low resistance and efficient gas exchange.

Question 3

During ECMO, a sudden rise in the pre-membrane pressure with a normal post-membrane pressure indicates:

Accepted Answer

Clot formation within the oxygenator fiber bundle

Answer

A rising gradient between pre- and post-membrane pressures signals increasing resistance within the oxygenator, most commonly due to clot accumulation in the fiber bundle.

Question 4

What is the typical target activated clotting time (ACT) range during standard ECMO anticoagulation?

Accepted Answer

180–220 seconds

Answer

Most ECMO centers target an ACT of 180–220 seconds to balance thrombosis prevention in the circuit against bleeding risk in the patient.

Question 5

The 'north-south syndrome' in VA-ECMO via femoral cannulation describes:

Accepted Answer

Differential hypoxia where upper body receives poorly oxygenated native cardiac output while lower body receives well-oxygenated ECMO flow

Answer

When the recovering heart ejects poorly oxygenated blood, a mixing zone forms in the aorta creating a differential: hypoxic upper body (brain, coronaries) versus oxygenated lower body from ECMO.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO Circuit Components and Management 3