What is the Difference Between PAO2 and SAO2?

The main difference between PAO2 and SAO2 lies in what each represents and how they measure oxygen content in the blood:

• PAO2: Partial pressure of oxygen (PaO2) measures the pressure at which oxygen dissolves in your blood. It is a driving pressure for oxygen molecules entering the red blood cell, and the higher the PaO2, the higher the SaO2. PaO2 is sensitive and non-specific indicator of the lungs' ability to exchange gases.
• SAO2: Arterial oxygen saturation (SaO2) is the percentage of total binding sites on arterial hemoglobin that are bound with oxygen and can never be more than 100%. SaO2 is determined by arterial blood gas (ABG) analysis, which is an invasive procedure. SaO2 is affected by factors such as PaCO2, body temperature, pH, and others, but it is unaffected by the content of hemoglobin, so anemia does not affect SaO2.

Both PAO2 and SaO2 are important in determining the amount of oxygen in a patient's blood and if it is adequate. They help medics assess the patient's oxygenation status and decide if supplemental oxygen therapy is needed.

Comparative Table: PAO2 vs SAO2

The difference between PaO2 and SaO2 lies in how they measure oxygen content in the blood. Here is a table summarizing the key differences:

In summary, PaO2 measures the actual oxygen content in arterial blood, while SaO2 measures the percentage of hemoglobin binding sites occupied by oxygen. The relationship between these two parameters is described by the oxyhemoglobin dissociation curve, which is affected by factors such as body temperature, pH, and PaCO2.