What is the Difference Between SAO2 and SPO2?

The main difference between SAO2 and SPO2 lies in the methods used to measure them and the blood components they represent. Here are the key differences:

1. SAO2: This is the oxygen saturation of arterial blood, meaning it represents the amount of oxygen bound to hemoglobin in the arteries. SAO2 levels are determined through arterial blood gas (ABG) analysis, which is an invasive procedure.
2. SPO2: This is the oxygen saturation measured by a pulse oximeter, a noninvasive device that estimates the oxygen-carrying capacity of hemoglobin in the blood. SPO2 represents the peripheral blood oxygen saturation levels, which are used to determine whether a patient requires mechanical oxygen support.

Typically, there is a discrepancy between SAO2 and SPO2, with the difference ranging from 2% to 3%. However, this discrepancy can be more significant in certain conditions, such as low perfusion states, arrhythmias, vasoconstriction, venous pulsations, and edema. In some cases, SPO2 can consistently underestimate SAO2 by an average of 5.3%. This discrepancy is due to various factors, including acid-base disorders or factors contributing to macro- or microcirculation.

Comparative Table: SAO2 vs SPO2

The main difference between SaO2 and SpO2 lies in the method of measurement and the type of blood they represent. Here is a table highlighting the differences between the two:

In general, pulse oximetry is a non-invasive and convenient method for estimating oxygen saturation. However, it may be less accurate in certain situations, such as when SpO2 values are below 82%. In contrast, arterial blood gas analysis provides a more accurate measure of arterial oxygen saturation but is invasive and requires a blood sample.