Ensuring sufficient fresh air delivery so you can tissues is a prime objective of acute/vital healthcare. There is no routinely available method for really overseeing muscle oxygenation; alternatively physicians must rely on offered indirect steps.

Although not the only factor to be considered, measurement of the amount of oxygen (O_dos) in blood is vital for the prediction of a patient’s tissue oxygen status. Blood oxygenation is most commonly assessed non-invasively by pulse oximetry. This allows convenient and safe continuous monitoring of oxygen saturation in peripheral (capillary) blood (SpO₂), but it has limitations.

Arterial blood gas analysis, the focus of this article, provides a fuller and more accurate ”gold standard” assessment of blood oxygenation status. It allows generation, not only of oxygen saturation (in arterial blood) sO₂(a), but a number of further oxygen-related parameters, including the partial pressure of oxygen in arterial blood, pO₂(a) and the total oxygen concentration of arterial blood, ctO₂(a).

Depending on the blood gas analyzer used, arterial oxygen saturation (sO₂(a)) is measured directly by CO-oximetry, or calculated from measured pO₂(a).

There is expert consensus that it is preferable to measure sO₂(a) rather than calculate it, and the main purpose of this article is to discuss the basis for this consensus, and highlight the inherent inaccuracy of calculated (estimated) sO₂(a), most particularly among the critically ill.