Pulmonary edema

Pulmonary edema can be defined as an abnormal accumulation of extravascular fluid in the lung parenchyma. This process leads to diminished gas exchange at the alveolar level, progressing to potentially causing respiratory failure. Its etiology is either due to a cardiogenic process with the inability to remove sufficient blood away from the pulmonary circulation or non-cardiogenic precipitated by injury to the lung parenchyma. It is an important pathologic feature in many disease processes, and hence learning the underlying disease process is crucial to guide its management. Clinical features include progressive worsening dyspnea, rales on lung auscultation, and worsening hypoxia.Pulmonary edema can be broadly classified into cardiogenic and noncardiogenic pulmonary edema.

Cardiogenic or volume-overload pulmonary edema arises due to a rapid elevation in the hydrostatic pressure of the pulmonary capillaries. This is typically seen in disorders involving left ventricular systolic and diastolic function (acute myocarditis including other etiologies of non-ischemic cardiomyopathy, acute myocardial infarction), valvular function (aortic/mitral regurgitation and stenosis in the moderate to the severe range), rhythm (atrial fibrillation with a rapid ventricular response, ventricular tachycardia, high degree, and third-degree heart block).

Noncardiogenic pulmonary edema is caused by lung injury with a resultant increase in pulmonary vascular permeability leading to the movement of fluid, rich in proteins, to the alveolar and interstitial compartments. Acute lung injury with severe hypoxemia is referred to as acute respiratory distress syndrome (ARDS) and is seen in various conditions directly affecting the lungs, such as pneumonia, inhalational injury, or indirectly, such as sepsis, acute pancreatitis, severe trauma with shock, multiple blood transfusions.

Difficulty breathing (dyspnea) or extreme shortness of breath that worsens with activity or when lying down.

A feeling of suffocating or drowning that worsens when lying down.

A cough that produces frothy sputum that may have blood in it.

A rapid, irregular heartbeat (palpitations)

The causes of pulmonary edema vary. Pulmonary edema falls into two categories, depending on where the problem starts.

If a heart problem causes the pulmonary edema, it's called cardiogenic pulmonary edema. Most often, the fluid buildup in the lungs is due to a heart condition.

If pulmonary edema is not heart related, it's called noncardiogenic pulmonary edema.

Sometimes, pulmonary edema can be caused by both a heart problem and a nonheart problem.

Understanding the relationship between the lungs and the heart can help explain why pulmonary edema may occur.

How the lungs work

Lungs contain many small, elastic air sacs called alveoli. With each breath, these air sacs take in oxygen and release carbon dioxide. Typically, this exchange of gases occurs without problems.

But sometimes, the alveoli fill with fluid instead of air. This keeps the bloodstream from taking in oxygen.

How the heart works

The left and right atria and left and right ventricles

Chambers and valves of the heartOpen pop-up dialog box

The typical heart is made of two upper and two lower chambers. The upper chambers (the right and left atria) receive incoming blood and pump it into the lower chambers (right and left ventricles). The lower chambers pump blood out of the heart.

Typically, blood without oxygen from all over the body enters the right atrium then the right ventricle. From there it's pumped through large blood vessels (pulmonary arteries) to the lungs. There, the blood releases carbon dioxide and picks up oxygen as it flows by the alveoli.

The oxygen-rich blood then returns to the left atrium through the pulmonary veins. It then flows through the mitral valve into the left ventricle. Finally, it leaves the heart through the body's main artery (aorta).

The heart valves keep blood flowing in the right direction. The aortic valve keeps the blood from flowing backward into the heart. From the aorta, the blood travels to the rest of the body.

Heart-related (cardiogenic) pulmonary edema

Cardiogenic pulmonary edema is caused by increased pressures in the heart.

It's usually a result of heart failure. When a diseased or overworked left lower heart chamber (left ventricle) can't pump out enough of the blood it gets from the lungs, pressures in the heart go up. The increased pressure pushes fluid through the blood vessel walls into the air sacs.

Medical conditions that can cause heart failure and lead to pulmonary edema include:

Coronary artery disease. Over time, the arteries that supply blood to the heart muscle can become narrow from fatty deposits (plaques). A slow narrowing of the coronary arteries can weaken the left ventricle.

Sometimes, a blood clot forms in one of these narrowed arteries. The clot blocks blood flow and damages part of the heart muscle, resulting in a heart attack. A damaged heart muscle can no longer pump as well as it should.

Cardiomyopathy. This term means heart muscle damage. With cardiomyopathy, the heart must pump harder, and pressures rise. Then the heart might not be able to work harder when needed, such as during exercise or with an infection or a rise in blood pressure. When the left ventricle can't keep up with the demands that are placed on it, fluid backs up into the lungs.

Heart valve problems. Narrowing (stenosis) of the aortic or mitral heart valves or a valve that leaks or doesn't close properly affects blood flow into the heart. A valve leak that develops suddenly might cause sudden and severe pulmonary edema.

High blood pressure (hypertension). Untreated or uncontrolled high blood pressure can enlarge the heart.

Other heart problems. Inflammation of the heart muscle (myocarditis), heart problems present at birth (congenital heart defects) and irregular heart rhythms (arrhythmias) also may cause pulmonary edema.

Kidney disease. High blood pressure due to narrowed kidney arteries (renal artery stenosis) or fluid buildup due to kidney disease can cause pulmonary edema.

Chronic health conditions. Thyroid disease and a buildup of iron (hemochromatosis) or protein (amyloidosis) also may contribute to heart failure and cause pulmonary edema.

Non-heart-related (noncardiogenic) pulmonary edema

High-altitude pulmonary edema

High-altitude pulmonary edemaOpen pop-up dialog box

Pulmonary edema that is not caused by increased pressures in the heart is called noncardiogenic pulmonary edema.

Causes of noncardiogenic pulmonary edema include:

Acute respiratory distress syndrome (ARDS). This serious disorder occurs when the lungs suddenly fill with fluid. Many conditions can cause ARDS, including severe injury (trauma), widespread infection (sepsis), pneumonia and severe bleeding.

Drug reaction or drug overdose. Many drugs — ranging from aspirin to illegal drugs such as heroin and cocaine — are known to cause pulmonary edema.

Blood clot in the lungs (pulmonary embolism). A blood clot moving from the blood vessels in the legs to the lungs can cause pulmonary edema.

Exposure to certain toxins. Inhaling toxins or breathing in some stomach contents when vomiting (aspiration) causes intense irritation of the small airways and air sacs, resulting in fluid buildup.

High altitudes. Pulmonary edema has been seen in mountain climbers, skiers, hikers and other people who travel to high elevations, usually above 8,000 feet (about 2,400 meters). High-altitude pulmonary edema (HAPE) generally occurs in those who don't take the days or weeks needed to become used to the elevation. But people who live at high altitudes can get HAPE with no elevation change if they have a respiratory illness.

Near drowning. Inhaling water causes fluid buildup in the lungs.

Negative pressure pulmonary edema. A blocked upper airway causes negative pressure in the lungs from trying to breathe through the blockage. With treatment, most people with this type of pulmonary edema recover in about 24 hours.

Nervous system conditions or surgeries. A type of pulmonary edema called neurogenic pulmonary edema can occur after a head injury, seizure or brain surgery.

Smoke inhalation. Smoke from a fire contains chemicals that damage the membrane between the air sacs and the capillaries. The damage allows fluid to enter the lungs.

Transfusion-related lung injury. Blood transfusions may cause fluid overload in the left ventricle, leading to pulmonary edema.

Viral illnesses. Viruses such as the hantavirus and dengue virus can cause pulmonary edema.

Hypertension (high blood pressure)

Kidney disease or kidney failure.

Obesity.

Diabetes.

Severe asthma.

Pneumonia.

Lung infection.

Sepsis (widespread infection) or blood infection.

Complications of pulmonary edema depend on the cause.

In general, if pulmonary edema continues, the pressure in the pulmonary artery can rise (pulmonary hypertension). Eventually, the heart becomes weak and begins to fail, and pressures in the heart and lungs go up.

Pulmonary edema complications may include:

Breathing difficulty

Swelling of the legs, feet and belly area

Buildup of fluid in the membranes that surround the lungs (pleural effusion)

Congestion and swelling of the liver

Immediate treatment is necessary for acute pulmonary edema to prevent death.

There is no way to fully prevent pulmonary edema. Those at high risk should seek immediate attention if they develop symptoms of the disorder.

The best way to try and prevent pulmonary edema is by taking good care of your health:

Get a pneumonia vaccine.

Get the flu vaccine, especially if you have heart problems or if you are an older adult.

Remain on diuretics after an episode of pulmonary edema to prevent a reoccurrence.

You can also decrease your risk for heart failure, the most common cause of pulmonary edema with the following steps:

Visit your doctor regularly.

Don’t smoke or use recreational drugs.

Get regular exercise.

Eat healthy foods.

Maintain a normal weight.