This process of delivery begins at the alveolar-capillary membrane of the lungs.

OXYGEN TRANSPORT IN BLOODĪ prime function of the respiratory and cardiovascular systems is delivery of inspired (atmospheric) oxygen to tissue cells. To understand how arterial blood gas results help in assessing patient risk of tissue hypoxia, a basic knowledge of oxygen transport in blood is necessary. Inadequate oxygen within tissues, called hypoxia, is the most common cause of cell injury/death and is central to, or at least a contributory factor in, the etiology and/or pathogenesis of most potentially life-threatening diseases/conditions seen in acute and critical care medicine. If the supply of oxygen is interrupted, this energy-generating process is curtailed or ceases, with resulting cell injury and, ultimately, cell death and organ failure. All tissue cells depend for their function and survival on the continuous generation of energy in the form of adenosine triphosphate (ATP) this ATP is generated within cells by aerobic metabolism of dietary fuels (principally glucose) to carbon dioxide and water. The article begins with an overview of the physiology of oxygen transport in blood that will help define oxygen saturation and explain its clinical significance. There is expert consensus that it is preferable to measure sO 2(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) sO 2(a), most particularly among the critically ill. It allows generation, not only of oxygen saturation (in arterial blood) sO 2(a), but a number of further oxygen-related parameters, including the partial pressure of oxygen in arterial blood, pO 2(a) and the total oxygen concentration of arterial blood, ctO 2(a).ĭepending on the blood gas analyzer used, arterial oxygen saturation ( sO 2(a)) is measured directly by CO-oximetry, or calculated from measured pO 2(a).

This allows convenient and safe continuous monitoring of oxygen saturation in peripheral (capillary) blood (SpO 2), but it has limitations.Īrterial blood gas analysis, the focus of this article, provides a fuller and more accurate ”gold standard” assessment of blood oxygenation status.

Blood oxygenation is most commonly assessed non-invasively by pulse oximetry. There is no routinely available method for directly monitoring tissue oxygenation instead clinicians must depend on available indirect measures.Īlthough not the only factor to be considered, measurement of the amount of oxygen (O 2) in blood is vital for the prediction of a patient’s tissue oxygen status. Ensuring adequate oxygen delivery to tissues is a prime objective of acute/critical medical care.

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