What is pulmonary edema?

Edema, in general, refers to swelling. This typically occurs when fluid from inside blood vessels seeps outside the blood vessel into the surrounding tissues, which can happen either because of the following:

Too much pressure in the blood vessels

Not enough proteins in the bloodstream to hold onto the fluid in the plasma (the part of the blood that does not contain any blood cells).

Pulmonary edema is when edema occurs in the lungs. The immediate area outside the small blood vessels in the lungs is occupied by very tiny air sacs called alveoli. This is where oxygen from the air is picked up by the blood passing by, and carbon dioxide in the blood is passed into the alveoli to be exhaled out. Alveoli typically have a thin wall that allows for this air exchange, and fluids are usually kept out of the alveoli unless these walls lose their integrity.

Pulmonary edema occurs when the alveoli fill up with excess fluid seeped out of the blood vessels in the lung instead of air. This can cause problems with the exchange of gas (oxygen and carbon dioxide), resulting in breathing difficulty and poor oxygenation of blood. Sometimes, this can be referred to as "water in the lungs" when describing the condition to patients.

Many different factors can cause pulmonary edema. It can be related to heart failure, called cardiogenic pulmonary edema, or related to other causes, referred to as non-cardiogenic pulmonary edema.

What causes pulmonary edema?

The causes of pulmonary edema can be broadly divided into cardiogenic and non-cardiogenic causes. Common causes are listed below.

Cardiogenic pulmonary edema results from high pressure in the blood vessels of the lungs due to poor heart function. Accumulation of more than the usual amount of blood in the blood vessels of the lungs can occur due to

This can, in turn, cause the fluid from the blood vessels to be pushed out to the alveoli as the pressure builds up.

Non-cardiogenic pulmonary edema can be caused by the following:

What are risk factors for pulmonary edema?

The risk factors for pulmonary edema are essentially the underlying causes of the condition. There isn't a specific risk factor for pulmonary edema other than risk factors for the causative conditions.

What are the symptoms of pulmonary edema?

The most common symptom of pulmonary edema is shortness of breath or breathlessness. This may be of gradual onset if the process develops slowly, or it can have a sudden onset in the case of acute pulmonary edema.

Other common symptoms may include:

Low blood oxygen levels (hypoxia) may be detected in patients with pulmonary edema. Furthermore, upon examination of the lungs with a stethoscope, the doctor may listen for abnormal lung sounds, such as rales or crackles (discontinuous short bubbling sounds corresponding to the splashing of the fluid in the alveoli during breathing).

When should I seek medical care for pulmonary edema?

Medical attention should be sought for anyone who is diagnosed with pulmonary edema of any cause.

Many cases of pulmonary edema require hospitalization, especially if the cause is acute. In some cases of chronic (long-term) pulmonary edema, for example with congestive heart failure, routine follow-up visits with the treating doctor may be recommended.

Most cases of pulmonary edema are treated by internal medicine doctors (internists), heart specialists (cardiologists), or lung doctors (pulmonologists).

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How is pulmonary edema diagnosed?

Pulmonary edema is typically diagnosed via chest X-ray. A normal chest radiograph (X-ray) consists of a central white area of the heart and its main blood vessels plus the bones of the vertebral column, with the lung fields showing as darker fields on either side, enclosed by the bony structures of the chest wall.

A typical chest X-ray with pulmonary edema may show a more white appearance over both lung fields than usual. More severe cases of pulmonary edema can demonstrate significant opacification (whitening) over the lungs with minimal visualization of the normal lung fields. This whitening represents the filling of the alveoli as a result of pulmonary edema, but it may give minimal information about the possible underlying cause.

To identify the cause of pulmonary edema, a thorough assessment of the patient's medical history and physical examination is needed as these often provide invaluable information regarding the cause.

Other diagnostics tools used in assessing the underlying cause of pulmonary edema include the measurement of plasma B-type natriuretic peptide (BNP) or N-terminal pro-BNP. This is a protein marker (a hormone) that will rise in the blood due to the stretch of the chambers of the heart. Elevation of the BNP nanogram (one billionth of a gram) per liter greater than a few hundred (300 or more) is highly suggestive of cardiac pulmonary edema. On the other hand, values less than 100 essentially rule out heart failure as the cause.

More invasive methods are occasionally necessary to distinguish between cardiac and noncardiac pulmonary edema in more complicated and critical situations. A pulmonary artery catheter (Swan-Ganz) is a thin, long tube (catheter) inserted into the large veins of the chest or the neck and advanced through the right-sided chambers of the heart and lodged into the pulmonary capillaries (small branches of the blood vessels of the lungs). This device has the capability of directly measuring the pressure in the pulmonary vessels, called the pulmonary artery wedge pressure.

A wedge pressure of 18 mmHg or higher is consistent with cardiogenic pulmonary edema,

Whereas a wedge pressure of less than 18 mmHg usually favors a non-cardiogenic cause of pulmonary edema.

A Swan-Ganz catheter placement and data interpretation is done only in the intensive care unit (ICU) setting.

What is the treatment for pulmonary edema?

The treatment of pulmonary edema largely depends on the cause and severity.

What are the complications of pulmonary edema?

Most complications of pulmonary edema arise from the complications associated with the underlying cause. More specifically, pulmonary edema can cause severely compromised oxygenation of the blood by the lungs. This poor oxygenation (hypoxia) can potentially lead to diminished oxygen delivery to different body organs, such as the brain.

Is it possible to prevent pulmonary edema?

Depending on the cause of pulmonary edema, some preventive measures can be taken. Long-term prevention of heart disease and heart attacks, slow elevation to high altitudes, or avoidance of drug overdose can be considered preventive.

On the other hand, some causes may not be completely avoidable or preventable, such as ARDS due to an overwhelming infection or trauma.

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References

Sovari, A.A. "Cardiogenic Pulmonary Edema." Medscape. July 23, 2020. <https://emedicine.medscape.com/article/157452-overview>.