Pulmonary edema is a form of swelling. General text dedicated to the swelling as a symptom can be found here.
Pulmonary edema is term for a dangerous condition, when fluid occurs in the lung tissue. The liquid is not inhaled; it is filtered into the lung alveoli from the local blood vessels. First, it is necessary to briefly tell about the anatomy of the lungs. The airways enter the lung tissue as the tube-like bronchi that branch in the lung tissue to smaller and smaller tubes. At the end of the tubes there are so-called alveoli. The alveoli are sac-like structures, whose walls are richly supplied by small local blood vessels. These vessels come from the right heart ventricle and they contain the deoxygenated blood. The thin walls of the alveoli enable the exchange of breathing gases. The molecules of oxygen enter the blood and carbon dioxide molecules enter the alveoli to be later exhaled out of the body. The oxygenated blood goes into the left side of the heart, which supplies practically all body tissues with oxygen-rich blood. The situation, when the alveolar walls for some reason allow filtration of the blood fluid, results in development of pulmonary edema.
What may be the cause of the above condition? The causes are numerous, but generally they can be summarized into two main categories.
This category includes all causes resulting from the impaired cardiac function. The main reason is the left-sided heart failure. The result is the inability of the heart pump to cope with the volume of pumped blood, which begins to accumulate in front of the left side of the heart, i.e. in the lung blood vessels. The local lung blood pressure increases and the fluid may begin to filter into the alveoli. This situation can be caused by an acute heart attack, valvular heart disease, arrhythmias, cardiomyopathies, etc. More information about the heart failure can be found in the relevant text.
These are causes unrelated to the heart. It should be noted that they are much rarer and I should mention them only marginally as the cardiac lung edema is much more frequent. This category includes conditions associated with a direct damage to the lining of the alveoli, which causes inflow of fluid into the alveolar sacs. Such damage can occur for example after inhalation of toxic and corrosive gases. In the following paragraphs I shall mention only the issue of cardiac causes.
The main manifestation is shortness of breath that worsens during physical activity and when lying in horizontal position. The patient therefore needs more pillows under his head and sleeps in a semi-sitting position. As the amount of fluid in the alveoli begins to increase, it manifests with wet cough and the person coughs up a pink-colored liquid. Acute forms may look very dramatically as the person suffers from a strong dyspnea and anxiety and the condition may be fatal without proper treatment.
The mentioned clinical symptoms and any information about previous heart disease may help the doctors. When listening to the lungs with a stethoscope, we hear typical sounds that occur in the lower parts of the lungs during the inspiration. Chest X-ray is an extremely effective and cheap imaging method that can inform us about the blood accumulation in the lung tissue.
In cardiogenic pulmonary edema, diuretics are the drugs of the first choice. The diuretics increase the urine production in kidneys and thus reduce the volume of fluid in the lung vessels. In acute condition, the diuretics are used in form of intravenous rapidly-acting substances. The treatment may be supported by oxygen therapy. In addition, it is necessary to treat the underlying condition, when possible. Severe acute cases may be treated under sedation with artificial lung ventilation that can create increased pressure in the airways to help to prevent the fluid from entering the alveoli.