The oxygen status of arterial human blood

Abstract

The oxygen status of arterial human blood is described at least by four variables: Oxygen partial pressure (pO₂, mmHg), oxygen saturation (sO₂, %), hemoglobin content (cHb, g/dL) and oxygen content (cO₂, mL/dL).

Beside perfusion, however, the oxygen supply of all organs is decisively determined by the mean capillary pO₂ which itself is primarily dependent on the arterial cO₂.

Therefore, the oxygen availability (cardiac output × caO₂, mL/min) may be described by the cO₂ value in arterial blood or those variables who determine the latter one. The diagnostic significance of the O₂ variables of the oxygen status consequently increases in the order of pO₂, sO₂ (cHb) and cO₂.

In arterial blood, oxygen partial pressure is the result of O₂ diffusion within the lungs into the blood (lung function). Oxygen saturation describes the portion of chemically bound oxygen expressed as O₂Hb in relation to total Hb (Hb + O₂Hb + COHb + MetHb). Oxygen content is the total amount of oxygen in blood chemically bound plus physically dissolved.

Under pathophysiological conditions the diagnostic significance becomes very clear.

Disturbances of lung function decreases all three variables, pO₂ (hypoxia), sO₂ (hypoxygenation) and cO₂ (hypoxemia), to produce hypoxic hypoxemia.

Carbon monoxide poisoning or methemoglobin formation decreases two variables, sO₂ and cO₂, where the pO₂ remains normal and results in toxic hypoxemia.

Anemia with a decrease in the hemoglobin content lowers cO₂ only, while pO₂ and sO₂ remain normal (anemic hypoxemia).

Key Words:

• Hb content
• hypoxemia
• hypoxygenation
• hypoxia
• O₂ content
• O₂ partial pressure
• O₂ saturation
• O₂ status.