What is the primary cause of hypoxemia?

The primary cause of hypoxemia is reduced oxygen delivery to the alveoli. In order for oxygen to enter the bloodstream and be transported to body tissues, it must first be delivered to the alveoli in the lungs. When there is an issue with oxygen reaching the alveoli—such as in cases of airway obstruction, lung diseases (like pneumonia or COPD), or impaired ventilation due to neuromuscular disorders—there can be a significant decrease in the amount of oxygen that can diffuse into the blood. This impaired exchange results in lower levels of oxygen in the arterial blood, leading to hypoxemia.

Understanding this mechanism is crucial for recognizing and treating conditions that affect oxygenation in patients. The other options offered do not relate directly to the physiological process of oxygen delivery resulting in hypoxemia.