SaO2 is the percentage of available binding sites on hemoglobin that are bound with oxygen in arterial blood. The O2 dissociation curve (and hence the SaO2 for a given PaO2) is affected by PaCO2, body temperature, pH and other factors.

What is the difference between SpO2 and SaO2?

The mean difference between SpO2 and SaO2 was -0.02% and standard deviation of the differences was 2.1%. From one sample to another, the fluctuations in SpO2 to arterial saturation difference indicated that SaO2 could not be reliably predicted from SpO2 after a single ABG.

What is the difference between PaO2 and PaO2?

PO2 is just partial pressure of oxgen in a given environment, such as room air. 21% O2 in standard barometric pressure of 760mmHg means usual PO2 in room air is 760 x 0.21 = 160mmHg. PAO2 is partial pressure of oxygen in alveoli. PaO2 is partial pressure of oxygen dissolved in (arterial) blood.