Oxygen Content
All calculations should be independently verified prior to clinical use. These calculators are intended to supplement, not replace, clinical judgment.
Calculate the arterial oxygen content (CaO2) from hemoglobin, oxygen saturation, and partial pressure of oxygen. SaO2 can be entered as a measured value or derived automatically from pO2 using the Severinghaus equation. Both the hemoglobin-bound and dissolved oxygen components are shown separately.
Arterial oxygen content is the sum of hemoglobin-bound and dissolved oxygen:
The constant 1.36 is the oxygen-carrying capacity of hemoglobin — the volume of O2 in mL (at 1 atmosphere) bound per gram of fully saturated hemoglobin. The exact value varies from 1.34 to 1.39 depending on the reference and derivation method; 1.36 is used here as the most commonly cited value.
The constant 0.0031 represents the solubility of oxygen in plasma (mL O2 per dL blood per torr). The dissolved term is normally small — at a typical PaO2 of 100 torr it contributes only 0.31 mL/dL — but becomes clinically significant at very high PaO2 (as in hyperbaric oxygen therapy) or in severe anaemia where the hemoglobin-bound component is markedly reduced.
Normal CaO2 is approximately 20 mL/dL. Venous oxygen content (CvO2) can be calculated by substituting SvO2 and PvO2. The arteriovenous oxygen difference (CaO2 − CvO2) combined with cardiac output yields oxygen delivery (DO2) and consumption (VO2).
See also the Oxygenation Index and Oxygen Saturation from pO2 calculators.
References
- Nunn JF. Nunn's Applied Respiratory Physiology. 4th ed. Butterworth-Heinemann; 1993.
- Severinghaus JW. Simple, accurate equations for human blood O2 dissociation computations. J Appl Physiol. 1979;46(3):599–602.
- West JB. Respiratory Physiology: The Essentials. 9th ed. Lippincott Williams & Wilkins; 2012.