Pulmonary oedema is the abnormal accumulation of fluid in the lung tissue and air sacs (alveoli), impairing gas exchange and causing severe breathlessness. It is most commonly caused by [left ventricular failure](/glossary/left-ventricular-failure/), in which the failing left ventricle cannot keep pace with blood returning from the lungs, causing pressure to rise in the pulmonary circulation and fluid to leak from the capillaries into the lungs.
Symptoms include sudden, severe breathlessness (often worse lying flat), a feeling of suffocation or drowning, a persistent cough (sometimes producing frothy or pink-tinged sputum), rapid heart rate, and anxiety. Acute pulmonary oedema is a medical emergency requiring immediate hospital treatment.
Causes include large heart attacks, [dilated cardiomyopathy](/glossary/dilated-cardiomyopathy/), severe valve disease, [hypertensive](/glossary/hypertension/) crisis, and, in the acute period after cardiac arrest, myocardial stunning. Non-cardiac causes (such as acute respiratory distress syndrome) also exist.
Treatment includes oxygen, intravenous diuretics (such as furosemide) to remove excess fluid, nitrates to reduce the pressure the heart pumps against, and, in severe cases, ventilatory support (non-invasive ventilation or mechanical ventilation). Once stabilised, underlying heart failure is treated according to cause and [ejection fraction](/glossary/ejection-fraction/).
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