Acute respiratory distress syndrome

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Acute respiratory distress syndrome

Respiratory system


Acute respiratory distress syndrome


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Acute respiratory distress syndrome

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USMLE® Step 1 style questions USMLE

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A 45-year-old man with a history of alcohol abuse is admitted for acute pancreatitis, and he becomes acutely short of breath on day two of his hospitalization. His temperature is 37°C (98.6°F), pulse is 108/min, respirations are 26/min, blood pressure is 110/94 mmHg, and oxygen saturation is 87% on room air. He is given supplemental O2 via non-invasive ventilation, but he later requires intubation due to persistent hypoxemia and concern for airway compromise. Chest x-ray demonstrates new bilateral opacities. His arterial blood gas on 100% FiO2 shows the following:  

Laboratory value  Result
Blood Gases, Serum 
pH  7.51 
 PCO2  23 mmHg 
 PO2  54 mm Hg 
Cardiac Enzymes, Serum 
Brain Natriuretic Peptide  (BNP)  <100 ng/dL (N = <100) 
 Troponin  <.03 ng/dL 
Which of the following physiologic parameters best confirms the diagnosis in this patient?

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Acute respiratory distress syndrome (ARDS) p. NaN

acute pancreatitis p. 406

eclampsia and p. 667

inhalational injury p. 701

Amniotic fluid emboli p. 697

acute respiratory distress syndrome as cause p. NaN

Pancreatitis p. 406

acute respiratory distress syndrome and p. NaN

Pneumonia p. 707

acute respiratory distress syndrome p. NaN

Respiratory distress syndrome p. 658


Acute Respiratory Distress Syndrome, or ARDS, is exactly what it sounds like.

‘Acute’ means that it happens rapidly.

‘Respiratory distress’ means that a person becomes unable to breathe and oxygenate their blood, and ‘syndrome’ means that it is a group of symptoms that may be caused by any number of underlying conditions.

In ARDS, the alveoli and the capillaries that surround them - the site of gas exchange in the lungs - are damaged by an inflammatory process like pneumonia or sepsis.

Air enters the lungs through a series of airways that branch and narrow until they end in clusters of alveoli, which look kinda like a bunch of grapes.

The alveoli are covered in nets of capillaries that allow gas exchange into and out of the blood.

Gas exchange happens efficiently between alveoli and capillaries because each of their walls is only one cell thick!

Capillaries are lined with a single layer of endothelial cells and alveoli are lined with a single layer of epithelial cells.

These cell layers are fused to one another by the basement membrane and surrounding the alveoli and blood vessels is connective tissue made up of mostly proteins and water - in a space called the interstitial space.

The alveolar epithelial cells—called pneumocytes—come in two types.

The vast majority are type I pneumocytes, which are thin and have a large surface area, a shape that allows oxygen and carbon dioxide to pass through them easily.

There are also type II pneumocytes scattered around which are smaller and thicker, and are important because they make surfactant, an oily secretion that coats the alveoli.


Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition that results in non-compliant lungs and poor blood oxygenation. It is associated with diffuse alveolar and endothelial injury. ARDS can be caused by a number of things, including pneumonia, sepsis, and trauma. Symptoms include shortness of breath, rapid breathing, and blue lips and fingernails.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Functional Food and Diseases" Centurion University of Technology and Management (2021)
  3. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  4. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  5. "Acute Respiratory Distress Syndrome" JAMA (2012)

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