Fluid in the lungs, medically called pulmonary edema, is caused by the accumulation of fluid in the tiny air sacs (alveoli) of the lungs, which hinders oxygen exchange. The causes are broadly categorized as cardiogenic (related to heart problems) or noncardiogenic (due to other factors).

Cardiogenic Causes

These are linked to heart problems where the heart fails to pump blood effectively, causing pressure buildup that forces fluid into the lungs. Common causes include:

• Heart failure, especially of the left ventricle
• Coronary artery disease and heart attacks
• Cardiomyopathy (heart muscle damage)
• Heart valve diseases (stenosis or leakage)
• High blood pressure (hypertension)
• Other cardiac problems like myocarditis or congenital heart defects
• Kidney disease that causes fluid retention

Noncardiogenic Causes

These result from injury or inflammation of the lung vessels, leading to leaky blood vessels and fluid entering the lungs without increased heart pressure. Some causes are:

• Pneumonia and severe infections
• Inhalation of toxins or chemicals
• Trauma to the chest or lung injury (e.g., pulmonary contusion)
• Adult respiratory distress syndrome (ARDS)
• High altitude pulmonary edema (HAPE)
• Negative pressure pulmonary edema from airway obstruction
• Certain cancers (lung, breast, ovarian), and cancer treatments

Both types impair oxygen exchange by filling the alveoli with fluid instead of air, leading to breathing difficulties and reduced oxygen in the blood.