What Is an Artificial Lung?
A Complete Guide to ECMO, VV-ECMO, and VA-ECMO
Modern medicine has achieved major breakthroughs in treating patients with life-threatening respiratory and cardiac failure. One of the most important of these breakthroughs is the artificial lung, commonly known as ECMO. This technology has saved countless lives in intensive care units, especially in severe respiratory failure, cardiogenic shock, and critical COVID-19 cases.
This article explains what an artificial lung is, how ECMO works, its main types, and the medical difference between VV-ECMO and VA-ECMO in a clear and professional manner.
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| A diagram illustrating the operation of the ECMO artificial lung and its types: VV-ECMO and VA-ECMO. |
What Is an Artificial Lung?
An artificial lung is an advanced medical device designed to temporarily replace the lungs’ essential function: gas exchange. Its main role is to deliver oxygen (O₂) into the blood and remove carbon dioxide (CO₂) from it. Unlike normal breathing, this process takes place outside the patient’s body, allowing damaged lungs—and sometimes the heart—to rest and recover.
The Basic Concept of Gas Exchange
In healthy lungs, air is inhaled and reaches the alveoli, where oxygen passes into the bloodstream and carbon dioxide is removed and exhaled. An artificial lung performs the same physiological process, but externally, when the lungs can no longer maintain adequate oxygenation on their own.
How Does an Artificial Lung Work?
Blood is withdrawn from the patient through a large cannula and directed into a system containing a highly specialized membrane. Oxygen flows on the opposite side of this membrane, allowing gas exchange to occur in a way similar to natural alveoli. The oxygenated blood is then returned to the patient’s circulation. This process runs continuously under strict monitoring in the intensive care unit.
ECMO: The Most Common Artificial Lung System
ECMO stands for Extracorporeal Membrane Oxygenation, meaning oxygenation of the blood outside the body using a membrane. It is used in severe and life-threatening conditions such as acute respiratory failure, acute respiratory distress syndrome (ARDS), severe pneumonia, complications after cardiac surgery, and critical COVID-19 infections. ECMO systems are divided into two main types, each serving a different medical purpose.
VV-ECMO: Respiratory Support Only
VV-ECMO, or Veno-Venous ECMO, is used when the lungs fail but the heart continues to function normally. Its role is limited to oxygenating the blood and removing carbon dioxide. It does not provide any direct cardiac support, as the heart remains responsible for pumping blood throughout the body.
In VV-ECMO, deoxygenated blood is drained from a large vein, most commonly the femoral or jugular vein. The blood passes through a pump and a membrane oxygenator, where oxygen is added and carbon dioxide is removed. The oxygenated blood is then returned to a central vein and subsequently pumped by the heart to the rest of the body. Unlike VA-ECMO, the blood does not enter the arterial system directly.
Cannulation is usually performed using a femoral vein for drainage and a jugular vein for reinfusion. In more advanced cases, a dual-lumen cannula may be used through the jugular vein, allowing both drainage and reinfusion through a single access point. This approach reduces complications and may allow limited patient mobility.
VV-ECMO is commonly used in severe ARDS, refractory respiratory failure, acute pneumonia, critical COVID-19 respiratory cases, carbon monoxide poisoning, and as a bridge to lung transplantation.
One of the main advantages of VV-ECMO is lung protection. It reduces ventilator pressures, minimizes ventilator-induced lung injury, and provides time for the lungs to heal. However, it carries risks such as bleeding due to anticoagulation, clot formation within the circuit, infection, cannula-related complications, and inadequate oxygenation if blood flow is insufficient.
In selected patients, VV-ECMO can be performed while the patient is awake. This approach, known as Awake ECMO, allows spontaneous breathing and may avoid mechanical ventilation in specific cases.
VA-ECMO: Combined Cardiac and Respiratory Support
VA-ECMO, or Veno-Arterial ECMO, provides both respiratory and circulatory support. It functions as an artificial lung by oxygenating the blood and as a temporary mechanical heart by actively supporting blood circulation. VA-ECMO is used when the heart fails, with or without associated lung failure.
In VA-ECMO, deoxygenated blood is withdrawn from the venous system and passes through a centrifugal pump and a membrane oxygenator. The oxygenated blood is then returned directly into an artery, allowing immediate distribution to vital organs such as the brain, heart, and kidneys. In these cases, the heart may be severely weakened or partially nonfunctional.
The most common configuration is peripheral VA-ECMO, where blood is drained from the femoral vein and returned through the femoral artery. A less common approach is central VA-ECMO, which involves drainage from the right atrium and reinfusion into the ascending aorta, typically performed after cardiac surgery.
VA-ECMO is indicated in cardiogenic shock, cardiac arrest requiring extracorporeal CPR, acute heart failure following myocardial infarction, acute myocarditis, post-cardiac surgery heart failure, and toxin- or drug-induced circulatory collapse.
The artificial lung, particularly through ECMO technology, represents a major life-saving advancement in modern critical care medicine. VV-ECMO is used when respiratory failure occurs with preserved cardiac function, while VA-ECMO is reserved for the most critical situations involving cardiac failure with or without lung dysfunction. In essence, VA-ECMO acts as an external heart and lung system, providing a vital bridge to recovery or further definitive treatment.
