What Causes Pulmonary Edema?
Pulmonary edema is often classified as cardiogenic or non-cardiogenic [due to a heart (cardiac) problem or due to a non-heart related issue respectively].
Cardiogenic Pulmonary Edema
Cardiogenic pulmonary edema is the most common type and is sometimes referred to as heart failure or congestive heart failure.
It may be helpful to understand how blood flows in the body to appreciate why fluid would "back up" into the lungs. The function of the right side of the heart is to receive blood from the body and pump it to the lungs where carbon dioxide is removed, and oxygen is deposited. This freshly oxygenated blood then returns to the left side of the heart which pumps it to the tissues in the body, and the cycle starts again.
Pulmonary edema is a common complication of atherosclerotic (coronary artery) disease. As the blood vessels that supply nutrients to the heart tissue progressively narrow, the heart muscle may not receive enough oxygen and nutrients to pump efficiently and adequately. This can limit the heart's ability to pump the blood it receives from the lungs to the rest of the body. If a heart attack occurs, portions of the heart muscle die and are replaced by scar tissue, further limiting the heart's pumping capability and leaving it unable to perform its function.
When the heart muscle is not able to pump effectively there is a backup of blood returning from the lungs to the heart; this backup causes an increase in pressure within the blood vessels of the lung, resulting in excess fluid leaking from the blood vessels into lung tissue.
Examples of other conditions in which heart muscle may not function adequately include (this list is not all-inclusive):
Two of the most common cardiomyopathies are ischemic (due to poor blood supply to the heart muscle as described above) and hypertensive. In hypertensive cardiomyopathy, poorly treated high blood pressure results in the thickening of the heart muscle to enable the heart to pump blood against that increased pressure. After a period of time, the heart may no longer be able to compensate and fails to keep up with the workload; as a result, fluid leaks out of the blood vessels into the lung tissue.
Another cause of pulmonary edema is mitral and aortic heart valve conditions. Normally, heart valves open and close at the appropriate time when the heart pumps, allowing blood to flow in the appropriate direction. In valvular insufficiency or regurgitation, blood leaks in the wrong direction. In stenosis of the heart valves, the valve becomes narrowed and doesn't allow enough blood to be pumped out of the heart chamber, causing pressure behind it. Failure of the mitral and aortic valves located on the left side of the heart can result in pulmonary edema.
Non-cardiogenic Pulmonary Edema
Non-cardiogenic pulmonary edema is less common and occurs because of damage to the lung tissue and subsequent inflammation of lung tissue. This can cause the tissue that lines the structures of the lung to swell and leak fluid into the alveoli and the surrounding lung tissue. Again, this increases the distance necessary for oxygen to travel to reach the bloodstream.
The following are some examples of causes of non-cardiogenic pulmonary edema.
- Kidney failure: In this situation, the kidneys do not remove excess fluid and waste products from the body, and the excess fluid accumulates in the lungs.
- Inhaled toxins: Inhaled toxins (for example, ammonia or chlorine gas, and smoke inhalation) can cause direct damage to lung tissue.
- High altitude pulmonary edema (HAPE): HAPE is a condition that occurs in people who exercise at altitudes above 8,000ft without having first acclimated to the high altitude. It commonly affects recreational hikers and skiers, but it can also be observed in well-conditioned athletes.
- Medication side effects: These may occur as a complication of aspirin overdose or with the use of some chemotherapy drug treatments.
- Illicit drug use: Non-cardiogenic pulmonary edema is seen in patients who abuse illicit drugs, especially cocaine and heroin.
- Adult respiratory distress syndrome (ARDS): ARDS is a major complication observed in trauma victims, in patients with sepsis, and shock. As part of the body's attempt to respond to a crisis, the antiinflammatory response attacks the lungs with white blood cells and other chemicals of the inflammatory response causing fluid to fill the air spaces of the lungs.
- Pneumonia: Bacterial or viral pneumonia infections are quite common; however, occasionally become complicated as a collection of fluid develops in the section of the lung that is infected.