pulmonary edema

Healthy lungs keep their air sacs dry, with only the thinnest film of fluid lining them for gas to cross. Pulmonary edema is what happens when fluid leaks out of the lung's tiny blood vessels and floods the surrounding tissue and air sacs, like a sponge soaked until air can no longer fill its pockets. Drowning the alveoli in fluid blocks oxygen from reaching the blood.

Fluid escapes the vessels for one of two broad reasons. Either the pressure inside the lung capillaries rises too high and pushes fluid out, most often because the left heart is failing to keep up, or the capillary walls become leaky from injury or inflammation, as in acute respiratory distress syndrome. The first is called cardiogenic and the second non-cardiogenic, and telling them apart guides treatment.

The hallmark symptoms are breathlessness, especially when lying flat, a sense of suffocation, and a cough sometimes producing frothy or pink-tinged sputum. Listening to the chest reveals crackles as air bubbles through the fluid. Treatment depends on the cause, with diuretics and pressure relief for the cardiac form and support of oxygen and breathing while the underlying problem is addressed.