ELSO Foundations Adult ECMO Flashcards
What are the components of an ECMO Circuit
Drainage Cannula
Pump Driver
Pump Console
Membrane Lung
Gas blender
Heat Exchanger
H20 Tubing
Return Cannula
Describe the features of a drainage cannula.
Long and multistage
Multiple holes both at the tip and along the length of the cannula
Describe the features of a return cannula.
Typically short and single stage
One hole at the tip of the cannula
What is the normal size for a return cannula in an adult?
17 to 19 French
What is the normal size for a drainage cannula in an adult?
21 and 25 French
Describe the Centrifugal Pump.
- Nonocclusive pump that propels blood using centrifugal forces
- When rotating the pump creates suction at the central hub
- Drives fluid to the periphery of the impeller
Describe the relationship of centrifugal pumps on preload and afterload.
Centrifugal pumps are preload dependent and afterload sensitive.
ECMO Pump
Explain Rotational Speed Concepts
- Blood is pumped forward at flow relative to resistance and rotational speed.
- While effective blood flow is dependent on the pump rotational speed, higher revolutions per minute, do not necessarily result in highter flow rates.
- Use the lowest RPM to achieve a certain flow
What is Cavitation?
While centrifugal pumps cannot generate very high positive pressures, they can generate significant and potentially unsafe **subatmospheric pressures of - 200 to - 300 mm Hg. **
This increases the risk of dissolved air being pulled out of the blood, a phenonmenon called “cavitation” that results in air bubbles comming out of the solution from the blood and causing cell damage.
Is it safe to clamp the ECMO Circuit?
It is safe to clamp the circuit with a running centrifugal pump
Centrifugal pumps cannot generate extreme positive pressure
Centrifugal pumps can generate unsafe negative pressures resulting in drainage insufficiency which can cause:
Cavitation
Hemolysis
Vessel wall damage
What is drainage insufficiency?
Extreme negative suction forces can cause blood vessels to collapse around the drainage cannula, potentially occluding drainage holes and damaging vessel intima.
What causes hemolysis on centrifugal pumps?
A clot or air is traped inside
The rotor is tilted
The revolutions per minute are high compared with the flow
Describe the membrane lung.
The membrane lung is an artificial lung responsible for oxygen uptake and carbon dioxide clearance.
It also modulates the temperature of the blood.
What are the the phases of the membrane lung
- Blood, gas, and water which are all physically separated.
- Blood from the drainage cannula enters the membrane lung and exits towards the return cannula.
- Gas from the blender enters and exits the membrane.
- Water from the heater enters and exits.
How does the membrane lung allow for gas exchange via diffusion according to pressure gradients?
Oxygen diffuses from the gas phase into the blood phase while carbon dioxide diffuses from the blood phase into the gas phase.
Describe polypropylene membranes.
Polypropylene membranes have a microporous design allowing for more efficient gas exchange but are prone to plasma leakage.
Describe Polymethylpentene (PMP) membranes
Polymethylpentene membranes have a nanoporous design with low risk for plasma leakage. They operate at low resistance and offer efficient gas exhange.
Modern membrane lungs primarily use PMP membranes.
What are the different types of membrane lung design.
Axial flow and transverse flow membrane lungs. Variations in design are associated with differences in priming volume, internal resistance, and working pressures.
What is the purpose of the blender in the ECMO circuit?
The blender provides fresh gas to the membrane lung, typically a mix of air and oxygen. This allows for the titration of FdO2, the device inlet oxygen fraction.
What are the three pressure regions in the ECMO circuit?
Drainage pressure
Pre-membrane lung pressure
Post-membrane lung pressure
Describe drainage pressure.
Drainage pressure is measured before the centrifugal pump inlet. The pressure is negative.
Describe Pre-membrane pressure.
Pre-membrane lung pressure is measured between the centrifugal pump outlet and near the membrane lung outlet. This pressure is positive.
Describe Post-membrane pressure.
Post-membrane lung pressure is measured at the membrane lung outlet. This pressure is positive but lower compared to the pre-membrane lung pressure.