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How can pulmonary edema interfere with oxygen exchange?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — human respiratory system The lungs serve as the gas-exchanging organ for the process of respiration.

In the human respiratory system, gas exchange relies on the efficient diffusion of oxygen and carbon dioxide across the thin, membranous barrier between the alveoli and the pulmonary capillaries.1

Pulmonary edema interferes with this process by causing an accumulation of watery blood plasma within the alveoli. Because these air sacs are intended to be filled with air to facilitate gas exchange, the presence of excess fluid physically obstructs the interface where oxygen would normally pass into the blood.21

As the alveoli become flooded with fluid, the effective surface area available for gas exchange is significantly reduced. This impairment prevents oxygen from reaching the blood efficiently, leading to symptoms such as difficulty breathing and a bluish tint to the skin (cyanosis), which indicates a lack of oxygen in the body's tissues. In severe cases, the inability to clear these secretions can be fatal, as the individual is effectively unable to exchange gases necessary for survival.2