Pulmonary edema

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Pulmonary edema



Pulmonary edema


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Pulmonary edema

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A 66-year-old nonbinary individual presents to the emergency department for evaluation of shortness of breath with exertion. The patient reports increasing shortness of breath over the past several weeks to the point where they can no longer climb a flight of stairs without becoming winded. Past medical history includes hypertension, hyperlipidemia, and deep vein thrombosis following a knee replacement surgery ten years ago. The patient has not seen a physician in years and is currently not on any medications. They currently smoke one pack of cigarettes daily. Temperature is 36.1°C (97.0°F), pulse is 78/min, respirations are 22/min, blood pressure is 188/92 mmHg, and O2 saturation is 91% on room air. Physical examination demonstrates an additional heart sound heard just after S2, and diffuse rales on lung auscultation. Jugular venous distension, pitting edema, and hepatomegaly are absent. A chest X-ray is obtained and demonstrated below. Which of the following best describes the pathophysiology of this patient’s pulmonary findings?  

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Acute pulmonary edema

opiod analgesics p. 572

Pulmonary edema

compliance in p. 689

consolidation in p. 302

heart failure p. 318

loop diuretics for p. 632

LV failure p. 316

mannitol p. 631

nitrates for p. 325

opioids for p. 572

preeclampsia and p. 667

renal failure p. 627

transfusion-related injury p. 112

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Pulmonary edema refers to the buildup of fluid in the lungs including the airways like the alveoli - which are the tiny air sacs - as well as in the interstitium, which is the lung tissue that’s sandwiched between the alveoli and the capillaries.

This space is mostly full of proteins, and when it starts filling up with fluid, it can make it hard for oxygen to cross over from the alveoli into the capillary, leaving the body hypoxic - or deprived of oxygen.

To understand pulmonary edema, let’s first talk about the three main factors that determine how fluid moves between the capillaries and interstitial fluid, which are the hydrostatic pressure, oncotic pressure and capillary permeability.

Hydrostatic pressure refers to the pressure felt by fluid in a confined space, pushing the fluid out of that space.

In the interstitial space, it’s the same thing as the blood pressure in the pulmonary capillaries, and because the pulmonary circulation is a low pressure system, the hydrostatic pressure is pretty low. But it’s still higher than the hydrostatic pressure exerted by the interstitial fluid of the lungs - which is almost zero.

So, to be clear, if hydrostatic pressure was the only factor involved, a lot of fluid would be continuously leaking out of the pulmonary capillaries into the lung’s interstitial space.

The next factor, though, is oncotic pressure; which is a type of osmotic pressure exerted by cells and proteins that can’t cross the capillary membrane and therefore tend to attract fluid.

The oncotic pressure is higher in the pulmonary capillaries than in the interstitial fluid, so it opposes the hydrostatic pressure.


Pulmonary edema is a condition in which fluid accumulates in the lungs, making it difficult for oxygen to pass through the alveoli and into the bloodstream. It is often due to the left ventricular heart failure to adequately remove blood from the pulmonary circulation, which is known as cardiogenic pulmonary edema. It can also be due to an injury to the lung parenchyma or vasculature of the lung - known as noncardiogenic pulmonary edema.

If not treated, pulmonary edema can lead to respiratory failure or cardiac arrest due to hypoxia. Treatment focuses on improving respiratory function, treating the underlying cause, and preventing and avoiding further damage to the lung.


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  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
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  6. "Causes of mortality in patients with the adult respiratory distress syndrome" undefined (undefined)
  7. "Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries" JAMA (2016)

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