ECMO - Extracorporeal Membrane Oxygenation Circuit Components and Management Questions and Answers — Questions and Answers
Question 1: An adult patient on VA ECMO for cardiogenic shock has a progressively increasing pressure gradient across the oxygenator, now measured at 120 mmHg. What is the most likely cause and appropriate initial action?
- Kinked return cannula; reposition the patient's leg.
- Hypovolemia; administer a fluid bolus.
- Oxygenator thrombus formation; prepare for an oxygenator change-out. (Correct answer)
- Pump head malfunction; switch to the backup pump immediately.
Correct answer: Oxygenator thrombus formation; prepare for an oxygenator change-out.
A progressively rising pressure gradient (transmembrane pressure) across the oxygenator, especially a value greater than 50-100 mmHg, is a strong indicator of clot formation within the oxygenator's hollow fibers. This increases resistance to blood flow and impairs gas exchange. The appropriate action is to prepare for a circuit or oxygenator change-out to prevent further complications like pump failure or embolization.
Question 2: During routine monitoring of a patient on VV ECMO, you observe 'chatter' or visible shaking in the venous drainage line, and the ECMO flow has intermittently decreased. Which of the following is the LEAST likely cause of this issue?
- Excessive pump RPM settings
- Hypovolemia or inadequate preload
- Cannula migration against a vessel wall
- Increased sweep gas flow (Correct answer)
Correct answer: Increased sweep gas flow
Chatter in the venous access line indicates access insufficiency, where the pump is trying to drain more blood than is available, causing the vein to collapse around the cannula. This can be caused by hypovolemia, excessive pump speed, or the cannula tip being positioned against a vessel wall. Sweep gas flow is related to gas exchange (CO2 removal) within the oxygenator and does not directly impact venous drainage or cause access insufficiency.
Question 3: A centrifugal pump is the most common type used in adult ECMO circuits. A key characteristic of a centrifugal pump is that its flow is:
- Independent of afterload and preload
- Preload dependent and afterload sensitive (Correct answer)
- Insensitive to afterload but dependent on preload
- Dependent on afterload but insensitive to preload
Correct answer: Preload dependent and afterload sensitive
Centrifugal pumps are non-occlusive pumps. Their output (flow) is dependent on the amount of blood available to enter the pump (preload) and sensitive to the resistance it has to pump against (afterload). For example, if afterload increases (e.g., due to a kink in the return line), the flow will decrease at the same RPM setting.
Question 4: The heat exchanger is an integral component of the ECMO circuit. What is its primary physiological purpose?
- To cool the blood to reduce metabolic demand
- To prevent clot formation within the oxygenator
- To maintain patient normothermia (Correct answer)
- To facilitate carbon dioxide removal
Correct answer: To maintain patient normothermia
Blood loses a significant amount of heat as it passes through the extracorporeal circuit, which is exposed to ambient room temperature. The primary function of the heat exchanger is to warm the blood before it returns to the patient, thereby maintaining normothermia.
Question 5: Which component of the ECMO circuit is directly responsible for both oxygenating the blood and removing carbon dioxide?
- Centrifugal pump
- Heat exchanger
- Blender
- Membrane oxygenator (Correct answer)
Correct answer: Membrane oxygenator
The membrane oxygenator, also called the membrane lung, is the component that performs gas exchange. It contains a semipermeable membrane that separates the blood path from the gas path, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out, mimicking the function of the alveoli in the lungs.
Question 6: In the event of a complete ECMO console power failure and inability to immediately restore power, what is the most critical emergency intervention to maintain some level of circuit flow?
- Clamping the circuit and manually ventilating the patient.
- Initiating cardiopulmonary resuscitation (CPR).
- Connecting the pump head to the emergency hand crank. (Correct answer)
- Administering a large bolus of intravenous fluids.
Correct answer: Connecting the pump head to the emergency hand crank.
In a catastrophic power loss, the pump will stop, leading to stasis of blood in the circuit and immediate loss of support. All ECMO systems have an emergency hand crank for this purpose. The operator must immediately transfer the pump head to the hand crank and begin rotating it to maintain blood flow, preventing thrombosis within the circuit and providing some level of support to the patient.
ECMO - Extracorporeal Membrane Oxygenation Circuit Components and Management Questions and Answers
An adult patient on VA ECMO for cardiogenic shock has a progressively increasing pressure gradient across the oxygenator, now measured at 120 mmHg.
What is the most likely cause and appropriate initial action?