How to calculate the total oxygen content of arterial blood
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.
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.
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Dissolved oxygen
Although the vast majority of arterial oxygen is transported in hemoglobin-bound form, a small amount is also transported dissolved in 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).
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.
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Recommended reading
- Grippi, MA. 1995. “Gas exchange in the lung”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 137–149)
- Grippi, MA. 1995. “Clinical presentations: gas exchange and transport”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 171–176)
- Grippi, MA and Tino, G. 2015. “Pulmonary function testing”. In: Fishman's Pulmonary Diseases and Disorders, edited by MA, Grippi (editor-in-chief), JA, Elias, JA, Fishman, RM, Kotloff, AI, Pack, RM, Senior (editors). 5th edition. New York: McGraw-Hill Education. (Grippi and Tino 2015, 502–536)
- Tino, G and Grippi, MA. 1995. “Gas transport to and from peripheral tissues”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Tino and Grippi 1995, 151–170)
- Wagner, PD. 2015. The physiologic basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases. Eur Respir J. 45: 227–243. PMID: 25323225
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