Symptoms, Causes, and Treatments for Hypoxemia

9. Understanding Hypoxemia

The key to knowing whether the lung is involved in hypoxemia is the difference between the arterial and alveolar oxygen levels. This distinction is often called the A-a gradient and is usually small. The oxygen contained in the alveolar air can be determined because it will be directly proportional to its fractional construction in the air. The arterial oxygen partial pressure is measured using a blood gas determination. Since the airways dilute and humidify the inhaled air, the vapor pressure of water reduces the barometric pressure of the air.