AssessmentsAcute respiratory distress syndrome
Acute respiratory distress syndrome
USMLE® Step 1 style questions USMLE
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:
|Blood Gases, Serum|
|PO2||54 mm Hg|
|Cardiac Enzymes, Serum|
|Brain Natriuretic Peptide (BNP)||<100 ng/dL (N = <100)|
Content Reviewers:Vincent Waldman, PhD
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.
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.
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.
The alveoli are so tiny that their walls end up being really close together.
The process of ARDS gets started when inflammatory molecules arrive in the lungs.
More specifically, these are cytokines like TNF-alpha and interleukin 1, that come through the bloodstream due to a systemic illness like a massive infection, or get released locally by alveolar macrophages in response to a lung injury.
Whatever the source, these cytokines cause capillary endothelial cells to secrete inflammatory molecules, and express adhesion molecules on their surface that help circulating immune cells to adhere or stick to them.
These neutrophils launch into inflammatory mode, releasing proteases, enzymes that digest protein, reactive oxygen molecules, that cause free radical damage, and cytokines, which perpetuate the cycle of inflammation.
As a result of this inflammation, a few important things happen. First, some inflammatory molecules are pro-coagulant, meaning they make the blood more likely to clot.
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.
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