# How to calculate the total oxygen content of arterial blood

In this short article, learn the essential concepts and how to calculate the total oxygen content of arterial blood.
Last update4th Dec 2020

## Bound oxygen

The principal form of oxygen transport in blood is as hemoglobin-bound. Each gram of hemoglobin can maximally bind 1.34 mL of oxygen. The oxygen-carrying capacity of the blood is calculated as the concentration of hemoglobin (in g / dL blood) times 1.34 mL O2 / g Hb.

Figure 1. Calculation for oxygen-carrying capacity of the blood, which shows that each gram of hemoglobin can maximally bind to 1.34 mL of oxygen.

In a healthy person, with a hemoglobin concentration of 15 g / dL blood, the oxygen carrying capacity is 20.1 mL O2 / dL blood.

But as we have seen, the actual amount of oxygen normally bound to hemoglobin does not always reflect 100% saturation. In fact, according to the oxyhemoglobin dissociation curve, arterial blood is about 97% saturated with oxygen when arterial oxygen tension is 100 mmHg.

Figure 2. The actual amount of bound oxygen to hemoglobin does not reflect complete saturation. The oxyhemoglobin dissociation curve shows that arterial blood is about 97% saturated with oxygen when arterial oxygen is 100 mmHg.
So the amount of oxygen bound is calculated as the carrying capacity times the oxygen saturation.Figure 3. Bound oxygen in the blood is calculated from carrying capacity and arterial oxygen saturation (SaO2).

## Dissolved oxygen

Although the vast majority of arterial oxygen is transported in hemoglobin-bound form, a small amount is also transported dissolved in plasma.

Figure 4. A small amount of oxygen is transported in the plasma.

According to Henry’s law, the amount of dissolved oxygen is proportional to the partial pressure of oxygen and its solubility coefficient. So, dissolved oxygen in the blood is calculated as the arterial oxygen tension (PaO2) times the solubility coefficient of oxygen (Sol O2 = 0.0031 mL O2 / dL blood / mmHg).

Figure 5. Henry’s law states that the amount of dissolved oxygen is proportional to the partial pressure of oxygen and its solubility coefficient. Therefore, it is calculated from the arterial oxygen tension (PaO2) and the solubility coefficient of oxygen (Sol O2).

In other words, at an arterial PO2 of 100 mmHg, 100 mL of arterial blood contains 0.31 mL of dissolved oxygen.

## Total oxygen content

The oxygen content of arterial blood (CaO2) is the sum of hemoglobin-bound and dissolved oxygen.

Figure 6. The oxygen content of arterial blood (CaO2) is equal to the sum of hemoglobin-bound oxygen (Hb-bound O2) and dissolved oxygen (O2).

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