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What Is ARDS? - Definition, Symptoms, Criteria & Treatment

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Acute respiratory distress syndrome (ARDS) is often a condition that results from another illness or trauma. Read this lesson to learn about ARDS, what the symptoms are, how it's treated, and the likely aftermath of experiencing ARDS.

Acute Respiratory Distress Syndrome (ARDS)

Fewer than 200,000 people suffer from acute respiratory distress syndrome (ARDS) each year, making it a relatively rare condition; however, it is serious and often life-threatening. Many of us take easy breathing for granted, and most of the time we don't even realize we're doing it.

When we inhale air through through the nose or mouth, it enters the body and goes into the trachea (windpipe). The trachea branches out into a number of tubes called bronchial tubes, and the bronchial tubes carry the air into the lungs. These bronchial tubes branch into smaller tubes called bronchioles, and then into even smaller air sacs called alveoli. The alveoli perform a very important job. They contain tiny capillaries that transfer oxygen from inhaled air into the blood, and also take carbon dioxide in the blood back to the lungs to be exhaled. They're so important that you have over 300 million alveoli in your body!

This image shows the alveoli at the ends of the bronchioles. The red and blue lines over the alveoli show the small capillaries where gases are exchanged.
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Why is this important? It's important because ARDS affects the alveoli, and prevents them from functioning properly. Specifically, ARDS causes fluids to leave the blood vessels and pool in the alveoli, preventing oxygen (and other gases) from being exchanged. In fact, it's very similar to what happens when the body experiences drowning. When fluid accumulates in the lungs, it not only blocks gas transfer, it also prevents the lungs from expanding fully. This all results in decreased oxygen concentration in the blood, ultimately affecting the entire body. Without adequate oxygen, tissues will start to die and major organs will begin to fail.

What Causes ARDS

Acute respiratory distress syndrome is usually caused by some type of trauma, or damage, to the lungs. This can happen if vomit is inhaled into the lungs (called aspiration), from inhaling hazardous chemicals, complications from a lung transplant, pneumonia, septic shock, or due to a physical injury. Of these causes, sepsis is the most common. Sepsis is a widespread infection in the blood vessels, so it can affect the entire body, particularly these small structures in the lungs. As you can see, ARDS is more often a symptom of another problem, rather than a condition that spontaneously occurs on its own.

ARDS Symptoms

The primary physical symptom of ARDS is fluid in the alveoli, and this causes a host of secondary symptoms, the most prevalent being difficulty breathing. As the body is deprived of oxygen, breathing often increases and becomes more labored. This can lead to low blood pressure, mental confusion, and physical fatigue. Decreased oxygen in the blood also causes the skin to develop a bluish tint (a condition called cyanosis).

Often, the underlying illness or injury that causes ARDS is so severe that a patient may not even recognize the symptoms of ARDS; they may attribute their symptoms to the underlying condition. That being said, ARDS symptoms usually occur within 24-48 hours of an injury or major illness like sepsis or pneumonia.

Diagnosing and Treating ARDS

If ARDS is suspected, a physician will run a number of tests. Blood analysis, urine analysis, chest x-rays, and a bronchoscopy are all possible options. A bronchoscopy is a procedure where a camera on a small tube is inserted through the mouth, down the trachea, and into the bronchial tubes leading to the lungs. The camera allows the doctor to look for fluid build-up without having to surgically open a patient up.

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