Pulmonary edema

Definition
By Mayo Clinic staff

Your lungs contain millions of small, elastic air sacs. With each breath, the air sacs take in oxygen and release carbon dioxide. Normally, the exchange of gases takes place without problems. But sometimes increased pressure in the blood vessels in your lungs forces fluid into the air sacs, preventing them from absorbing oxygen — a condition called pulmonary edema.

In most cases, heart problems cause pulmonary edema. But fluid can accumulate for other reasons, including pneumonia, exposure to certain toxins and medications, and exercising or living at high elevations.

Acute pulmonary edema is a medical emergency requiring immediate care. Although pulmonary edema can sometimes prove fatal, the outlook is often good when you receive prompt treatment for pulmonary edema along with therapy for the underlying proble

Symptoms

Depending on the cause, pulmonary edema symptoms may appear suddenly or develop slowly over weeks or months.

Signs and symptoms that come on suddenly are usually severe and may include:

* Extreme shortness of breath or difficulty breathing
* A feeling of suffocating or drowning
* Wheezing or gasping for breath
* Anxiety, restlessness, a sense of apprehension
* A cough that produces frothy sputum that may be tinged with blood
* Excessive sweating
* Pale skin
* Chest pain when pulmonary edema is caused by coronary artery disease

If you develop any of these signs or symptoms, call 911 or emergency medical assistance right away. Pulmonary edema can be fatal if not treated.

Signs and symptoms that develop more gradually include:

* Difficulty breathing when you're lying flat as opposed to sitting up.
* Awakening at night with a breathless feeling.
* Having more shortness of breath than normal when you're physically active.
* Significant weight gain when pulmonary edema develops as a result of congestive heart failure, a condition in which your heart pumps too little blood to meet your body's needs. The weight gain is from accumulation of fluid in your body, especially in your legs.

Causes

Two major airways (bronchi) carry air into your lungs. These airways subdivide into smaller airways (bronchioles) that finally end in clusters of tiny air sacs called alveoli. These air sacs inflate like miniature balloons every time you inhale.

Wrapped around each air sac are capillaries that connect the arteries and veins in your lungs. The capillaries are so narrow that red blood cells have to pass through them in single file. Each red blood cell absorbs oxygen, while the plasma — the fluid containing the red blood cells — releases carbon dioxide as well as absorbs some of the oxygen.

But in certain circumstances, the alveoli fill with fluid instead of air, preventing oxygen from being absorbed into your bloodstream. A number of factors can cause fluid to accumulate in your lungs, but most have to do with your heart (cardiac pulmonary edema). Understanding the relationship between your heart and lungs can help explain why.

How your heart works
Your heart is composed 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. The lower chambers, the more muscular right and left ventricles, pump blood out of your heart. The heart valves — which keep blood flowing in the correct direction — are gates at the chamber openings.

Normally, deoxygenated blood from your body enters the right atrium and flows into the right ventricle, where it's pumped through large blood vessels (pulmonary arteries) to your lungs. There, the blood releases carbon dioxide and picks up oxygen. The oxygen-rich blood then returns to the left atrium through the pulmonary veins, flows through the mitral valve into the left ventricle, and finally leaves your heart through another large artery, the aorta. The aortic valve at the base of the aorta keeps the blood from flowing backward into your heart. From the aorta, the blood travels to the rest of your body.

What goes wrong
Cardiac pulmonary edema — also known as congestive heart failure — occurs when the left ventricle isn't able to pump out enough of the blood it receives from your lungs. As a result, pressure increases inside the left atrium and then in the pulmonary veins and capillaries, causing fluid to be pushed through the capillary walls into the air sacs.

Congestive heart failure can also occur when the right ventricle is unable to overcome increased pressure in the pulmonary artery, which usually results from left heart failure, chronic lung disease or high blood pressure in the pulmonary artery (pulmonary hypertension).

Medical conditions that can cause the left ventricle to become weak and eventually fail include:

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Coronary artery disease. Over time, the arteries that supply blood to your heart can become narrow from fatty deposits (plaques). A heart attack occurs when a blood clot forms in one of these narrowed arteries, blocking blood flow and damaging the portion of your heart muscle supplied by that artery. The result is that the damaged heart muscle can no longer pump as well as it should.

Although the rest of your heart tries to compensate for this loss, it's either unable to do so effectively or it's weakened by the extra workload. When the pumping action of your heart is weakened, blood backs up into your lungs, forcing fluid in your blood to pass through the capillary walls into the air sacs.
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Cardiomyopathy. When your heart muscle is damaged by causes other than blood flow problems, the condition is called cardiomyopathy. Often, cardiomyopathy has no known cause, although it sometimes runs in families. Less common causes include infections (myocarditis), alcohol abuse and the toxic effects of drugs such as heroin and some types of chemotherapy.

Because cardiomyopathy weakens the left ventricle — your heart's main pump — your heart may not be able to respond to conditions that require it to work harder, such as a surge in blood pressure or infections. When the left ventricle can't keep up with the demands placed on it, fluid backs up into your lungs.
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Heart valve problems. In mitral valve disease or aortic valve disease, the valves that regulate blood flow either don't open wide enough (stenosis) or don't close completely (insufficiency). This allows blood to flow backward through the valve. When the valves are narrowed, blood can't flow freely into your heart and pressure in the left ventricle builds up, causing the left ventricle to work harder and harder with each contraction.

The increased pressure extends into the left atrium and then to the pulmonary veins, causing fluid to accumulate in your lungs. On the other hand, if the mitral valve leaks, some blood is backwashed toward your lung each time your heart pumps. If the leakage develops suddenly, you may develop sudden and severe pulmonary edema.
* High blood pressure (hypertension). Untreated or uncontrolled high blood pressure causes a thickening of the left ventricular muscle, and accelerates coronary artery disease.

Noncardiac pulmonary edema
Not all pulmonary edema is the result of heart disease. Fluid may also leak from the capillaries in your lungs' air sacs because the capillaries themselves become more permeable or leaky, even without the buildup of back pressure from your heart. In that case, the condition is known as noncardiac pulmonary edema because your heart isn't the cause of the problem. Some factors that can cause increased capillary permeability leading to noncardiac pulmonary edema are:

* Lung infections. When pulmonary edema results from lung infections, such as pneumonia, the edema occurs only in the part of your lung that's inflamed.
* Exposure to certain toxins. These include toxins you inhale — such as chlorine, ammonia or nitrogen dioxide — as well as those that may circulate within your own body. For example, women giving birth may develop pulmonary edema when amniotic fluid reaches the lungs through the veins of the uterus (amniotic fluid embolism).
* Kidney disease. When your kidneys can't remove waste effectively, excess fluid can build up, causing pulmonary edema.
* Smoke inhalation. Smoke contains chemicals that damage the membrane between the air sacs and the capillaries, allowing fluid to enter your lungs.
* Adverse drug reaction. Many drugs — ranging from narcotics such as heroin to diabetes medications and chemotherapy drugs — are known to cause noncardiac pulmonary edema.
* Acute respiratory distress syndrome (ARDS). This serious disorder occurs when your lungs suddenly fill with fluid and inflammatory blood cells. Many conditions can cause ARDS, including severe injuries (trauma), systemic infection (sepsis), pneumonia and shock. ARDS sometimes develops after extensive surgery.
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High altitudes. Mountain climbers and people who live in or travel to high-altitude locations run the risk of developing high-altitude pulmonary edema (HAPE). This condition — which typically occurs at elevations above 8,000 feet — can also affect hikers or skiers who start exercising at higher altitudes without first becoming acclimated. But even people who have hiked or skied at high altitudes in the past aren't immune.

Although the exact mechanism isn't completely understood, HAPE seems to develop as a result of increased pressure from constriction of the pulmonary capillaries. Symptoms include headaches, insomnia, fluid retention, cough and shortness of breath. Without appropriate care, HAPE can be fatal.

Tests and diagnosis

Because pulmonary edema requires prompt treatment, you'll initially be diagnosed on the basis of your symptoms and a physical exam. You may also have blood drawn — usually from an artery in your wrist — so that it can be checked for the amount of oxygen and carbon dioxide it contains (arterial blood gas concentrations).

Once your condition is more stable, your doctor will ask about your medical history, especially whether you have ever had cardiovascular or lung disease. You'll also likely have a chest X-ray, which can help support a diagnosis of pulmonary edema. And you may have further tests to determine why you developed fluid in your lungs. These tests may include:

* Electrocardiography (ECG). This noninvasive test can reveal a wide range of information about your heart. During an ECG, patches attached to your skin receive electrical impulses from your heart. These are recorded in the form of waves on graph paper or a monitor. The wave patterns show your heart rate and rhythm, and whether areas of your heart show diminished blood flow.
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Echocardiography (diagnostic cardiac ultrasound exam). Another noninvasive test, echocardiography uses a wand-shaped device called a transducer to generate high-frequency sound waves that are reflected from the tissues of your heart. The sound waves are then sent to a machine that uses them to compose images of your heart on a monitor.

The test can help diagnose a number of heart problems, including valve problems, abnormal motions of the ventricular walls, fluid around the heart (pericardial effusion) and congenital heart defects. It also accurately measures the amount of blood your left ventricle ejects with each heartbeat (ejection fraction, or EF). Although a low EF often indicates a cardiac cause for pulmonary edema, it's possible to have cardiac pulmonary edema with a normal EF.
* Transesophageal echocardiography (TEE). In a traditional cardiac ultrasound exam, the transducer remains outside your body on the chest wall. But in TEE, a soft, flexible tube with a special transducer tip is inserted through your mouth and into your esophagus — the passage leading to your stomach. The esophagus lies immediately behind your heart, which allows for a closer and more accurate picture of your heart and central pulmonary arteries. You'll be given a sedative to make you more comfortable and prevent gagging. You may have a sore throat for a few days after the procedure, and there's a slight risk of perforation or bleeding from the esophagus.
* Pulmonary artery catheterization. If other tests don't reveal the reason for your pulmonary edema, your doctor may suggest a procedure to measure the pressure in your lung capillaries (wedge pressure). During this test, a small, balloon-tipped catheter is inserted through a vein in your leg or arm into a pulmonary artery. The catheter has two openings connected to pressure transducers. The balloon is inflated and then deflated, giving pressure readings.

Complications

If pulmonary edema persists, it can raise pressure in the pulmonary artery and eventually the right ventricle begins to fail. The right ventricle has a much thinner wall of muscle than does the left side. The increased pressure backs up into the right atrium and then into various parts of your body, where it can cause:

* Leg swelling (edema)
* Abdominal swelling (ascites)
* Buildup of fluid in the membranes that surround your lungs (pleural effusion)

When not treated, acute pulmonary edema can be fatal. In some instances it may be fatal even if you receive treatment. The outcome depends in part on the condition of your heart and lungs before you developed edema and on the amount of fluid in your lungs. Drug-induced pulmonary edema can be a cause of death in people who abuse narcotics.

Treatments and drugs

Administering oxygen is the first step in the treatment for pulmonary edema. You usually receive oxygen through a face mask or nasal cannula — a flexible plastic tube with two openings that deliver oxygen to each nostril. This should ease some of your symptoms. Sometimes it may be necessary to assist your breathing with a machine.

Depending on your condition and the reason for your pulmonary edema, you may also receive one or more of the following medications:

* Preload reducers. Doctors commonly use nitroglycerin and diuretics, such as furosemide (Lasix), to treat pulmonary edema. These medications dilate the veins in your lungs and elsewhere in your body, which decreases fluid pressure going into your heart and lungs.
* Morphine (Astramorph, Roxanol). This narcotic, for years a mainstay in treating cardiac pulmonary edema, may be used to relieve shortness of breath and associated anxiety. But some doctors believe that the risks of morphine may outweigh the benefits and are more apt to use other, more effective, drugs.
* Afterload reducers. These drugs dilate the peripheral vessels and take a pressure load off the left ventricle. Some examples of afterload reducer medications include nitroprusside (Nitropress), enalapril (Vasotec) and captopril (Capoten).
* Aspirin. Your doctor may recommend starting aspirin therapy if you're not already taking it. Aspirin helps thin your blood so that it moves through your small blood vessels more easily.
* Blood pressure medications. If you have high blood pressure when you develop pulmonary edema, you'll be given medications to control it. On the other hand, if your blood pressure is too low, you're likely to be given drugs to raise it.

Treating high-altitude pulmonary edema (HAPE)
If you're climbing or traveling at high altitudes and experience mild symptoms of HAPE, descending a few thousand feet should relieve your symptoms. Oxygen also is helpful. When symptoms are more severe, you'll likely need help in your descent. A helicopter rescue may be necessary for the most serious cases.

Sometimes, however, immediate rescue isn't possible. With this in mind, researchers have devised several experimental therapies. In one, the distressed climber is placed in an airtight bag known as a hyperbaric bag, which is then pumped with air, simulating the air pressure at a lower altitude. A night's sleep in the bag seems to relieve symptoms — at least temporarily.

Some climbers take the prescription medication acetazolamide (Diamox) to help treat or prevent symptoms of HAPE. Diamox can occasionally have side effects — including tingling or burning in the hands, feet and mouth, confusion, diarrhea, nausea, and thirst.

Prevention

Pulmonary edema often isn't preventable, but these measures can help reduce your risk:

Preventing cardiovascular disease
Cardiovascular disease is the leading cause of pulmonary edema. You can reduce your risk of many kinds of heart problems by following these suggestions:

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Control your blood pressure. High blood pressure (hypertension) can lead to serious conditions such as stroke, cardiovascular disease and kidney failure. Most adults should have their blood pressure checked at least once every two years. This is a noninvasive and painless procedure using an inflatable cuff that wraps around your upper arm. The test takes just a few minutes.

A resting blood pressure reading below 120/80 millimeters of mercury (mm Hg) is considered normal. If your resting blood pressure is consistently 140/90 mm Hg or higher, you have high blood pressure. A reading in between these levels places you in the prehypertensive category.

In many cases, you can lower your blood pressure or maintain a healthy level by getting regular exercise, eating a diet rich in fresh fruits, vegetables and low-fat dairy products, and limiting alcohol and coffee.
* Watch your blood cholesterol. Cholesterol is one of several types of fats essential to good health. But too much cholesterol can be too much of a good thing. Higher than normal cholesterol levels can cause fatty deposits to form in your arteries, impeding blood flow and increasing your risk of vascular disease. But lifestyle changes can often keep your cholesterol levels low. This includes limiting fats — especially saturated fats — eating more fiber, fish, and fresh fruits and vegetables, exercising regularly, stopping smoking, and drinking in moderation.
* Don't smoke. If you smoke, the single most important thing you can do for your heart and lung health is to stop. Continuing to smoke increases your risk of a second heart attack or heart-related death and also increases your risk of lung cancer and other lung problems such as emphysema. What's more, you're at risk even if you don't smoke but live or work with someone who does. Exposure to secondhand smoke is a contributing factor to coronary artery disease. If you can't stop smoking by yourself, ask your doctor to prescribe a treatment plan to help you quit.
* Eat a heart-healthy diet. Fish is one of the cornerstones of a heart-healthy diet — it contains omega-3 fatty acids, which help improve blood cholesterol levels and prevent blood clots. It's also important to eat plenty of fruits and vegetables, which contain antioxidants, vitamins and minerals that help prevent everyday wear and tear on your coronary arteries. Limit your intake of all types of fats, especially animal (saturated) and trans fats (hydrogenated oils).
* Limit salt. It's especially important to limit your salt intake if you have heart disease. In some people with severely impaired left ventricular function, excess salt — even in a single meal or a bag of chips — may be enough to trigger congestive heart failure. If you're having a hard time cutting back on salt, it may help to talk to a dietitian. He or she can help point out low-sodium foods as well as offer tips for making a low-salt diet interesting and good tasting.
* Exercise regularly. Exercise is vital for a healthy heart. Regular aerobic exercise helps maintain a healthy weight, controls blood pressure and cholesterol levels, helps prevent diabetes and maintains muscle tone. If you're not used to exercise, start out slowly and build up gradually.
* Maintain a healthy weight. Being even slightly overweight increases your risk of cardiovascular disease. On the other hand, losing only 10 percent of your body weight can lower your blood pressure, cholesterol and reduce your risk of diabetes.
* Get enough folic acid (folate). An essential B vitamin, folate may reduce blood levels of homocysteine, an amino acid that builds and maintains tissues. Too much homocysteine can promote the formation of plaques in your arteries. To get 400 micrograms of folate a day, eat green, leafy vegetables, citrus fruits, legumes, peanuts and cereal grains. If you're not sure how much folate you're getting from your diet, talk to your doctor about a folic acid supplement, or choose a multivitamin supplement that contains at least 400 micrograms of folic acid.
* Manage stress. To reduce your risk of heart problems, try to reduce your stress levels. Rethink workaholic habits and find healthy ways to minimize or deal with stressful events in your life.

Preventing HAPE
If you travel or climb at high altitudes, acclimate yourself slowly. Although recommendations vary, most experts advise ascending no more than 1,000 or 2,000 feet a day once you reach 8,000 feet. In addition, it's important to drink plenty of water to stay hydrated. The higher you ascend the more rapidly you breathe, which means you lose larger amounts of water in the air you exhale from your lungs. Finally, although being physically fit won't necessarily prevent HAPE, people in good condition tend to be less stressed at high altitudes.