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.