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Discussion

Can someone please explain the difference PO2 and PaO2?

Hi all,

I can't understand what is the difference between PO2 and Pa02.

I know that PaO2 is the partial pressure of oxygen in blood.

PO2 is partial pressure of Oxygen.

Are they interchangeable?

For example in many textbooks (and websites) I have read, about the oxygen dissocation curve,

The x-axis is PO2.

In the discussion, they state "it describes the relationship between the sat of Hb and the patrial pressure of (PO2) in the blood. Due to the shape of the curve, a small drop in PaO2 below 8kPa will cause a marked fall in SaO2."

In the same paragraph, they made reference to both PO2 and PaO2.

Thank you for your help.

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    They are used interchangeably, but are not technically the same (from my understanding). For the purposes of your test, treat them the same.

    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. Partial pressure of a gas dissolved in a liquid depends on the qualities of the liquid and the concentration of the gas. This is where the dissociation curve comes in - its the relationship between the pp and total content of O2 in the blood.

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