Pulmonary edema is a condition where fluid accumulates within the lung tissue. The many causes of pulmonary edema can be separated into two distinct groups: cardiogenic and noncardiogenic. Cardiogenic causes include such issues as heart abnormalities, congestive heart failure and myocardial ischemia. Noncardiogenic causes include a vast number of conditions, including lung injuries, sepsis, pancreatitis and reactions to transfusions. The extent of the pulmonary edema depends on osmotic and hydrostatic forces within the pulmonary capillaries.
The cardiogenic causes of pulmonary edema include a variety of heart abnormalities that result in an increase in the pulmonary venous pressure. This increase shifts the delicate balance between the interstitial tissue and the pulmonary capillaries. Thus, the hydrostatic pressure elevates, promoting the collection of fluid into the capillaries and thereafter into the alveoli. Alveoli are tiny air sacs that easily fill with fluid, resulting in shortness of breath and coughing.
Cardiogenic causes of pulmonary edema also encompass such heart conditions as congestive heart failure, myocardial ischemia, heart attack and valvular abnormalities that result in volume overloads of the left ventricle. The valvular causes of pulmonary edema include mitral valve stenosis, mitral valve regurgitation and aortic insufficiency. Ventricular septal defects, which are holes within the cardiac muscle separating the two lower chambers of the heart, can also result in pulmonary edema.
Noncardiogenic causes of pulmonary edema cover a wide variety of conditions, including direct injury to the lungs; hematogenous injury, or a collection of blood within lung tissue; elevations of hydrostatic pressure; and chemical agents. Edema increases inside the lungs from leakage of proteins through damaged capillary linings. Fluid follows the leaking proteins due to oncotic forces causing a dysfunction of the surfactant-lined alveoli. Thus, noncardiogenic pulmonary edema often manifests with severe hypoxia, bluish skin discoloration and markedly decreased lung performance.
Pulmonary edema caused by direct injuries to the lungs can result from aspiration, smoke inhalation and chest trauma. Injuries also can be caused by pulmonary contusion, pneumonia, pulmonary embolism and oxygen toxicity, which occurs from breathing high concentrations of oxygen at high atmospheric pressures. Hematogenous injuries causing pulmonary edema include an assortment of diseases. These serious conditions include sepsis, disseminated intravascular coagulation (DIC), pancreatitis, multiple transfusions with transfusion reactions, non-thoracic trauma and extended time on cardiopulmonary bypass during surgeries.
Some lung injuries causing pulmonary edema are due to elevated hydrostatic pressure. For example, high altitude pulmonary edema (HAPE) is an acute mountain illness that occurs when persons ascend to high elevations without proper acclimation. Of all the causes of pulmonary edema, HAPE has the simplest treatment: descend to lower altitudes.
Other elevations of hydrostatic pressure can be caused by increased intracerebral pressure, which is called neurogenic pulmonary edema. Pulmonary edema also can result from lung re-expansion after a lung collapse. Some chemical causes of pulmonary edema include radiographic contrast allergies, salicylate intoxication and inhaled toxins, such as occurs in smoke inhalation.
