What is the primary cause of hypoxemia experienced in ARDS?

The primary cause of hypoxemia in Acute Respiratory Distress Syndrome (ARDS) is fluid accumulation in the alveoli. In ARDS, there is a significant inflammatory response that leads to increased permeability of the alveolar-capillary membrane. This causes fluid to leak into the alveoli, resulting in pulmonary edema. The accumulation of fluid impairs gas exchange, as it prevents oxygen from effectively diffusing into the blood and carbon dioxide from being adequately expelled. Consequently, this fluid-filled state significantly decreases the ventilation-perfusion ratio, leading to hypoxemia—defined as low levels of oxygen in the blood. Addressing the fluid accumulation is critical in the management of ARDS to restore adequate oxygenation.