PaO2 question

zzyzx

zzyzx

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If a healthy young person was breathing 100% Fio2 for an extended period of time at sea level, what is the highest PaO2 value they could reach?
 
zzyzx said:
If a healthy young person was breathing 100% Fio2 for an extended period of time at sea level, what is the highest PaO2 value they could reach?
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663

Had to be able to do the math at one time, now I use Google. And then I checked with the wife (pulm doc).

Edit: I used this website for a refresher on the equation
PAO2 = FIO2(PB-47) - 1.2(PaCO2)

To do the actual calculation, I used an on-line calculator
 
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655 mmhg
 
KellyBracket said:
Well, you had me sweating that I forgot the normal PaCO2 or something!
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Nope . Just me using wrong numbers

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KellyBracket said:
663

Had to be able to do the math at one time, now I use Google. And then I checked with the wife (pulm doc).

Edit: I used this website for a refresher on the equation
PAO2 = FIO2(PB-47) - 1.2(PaCO2)

To do the actual calculation, I used an on-line calculator
Click to expand...

Just to check my understanding, this assumes normal body temperature, correct? (-47 is the presumed partial pressure of H2O at said temp?)

Wouldn't this actually yield the PAO2 rather than the PaO2?
 
Wow, thanks for all the quick replies!

So, in a healthy person, how would this very high PaO2 affect the amount of oxygen actually available to the tissues? The SpO2 wouldn't change to any significant amount since it's already near 100%, but there would be more oxygen dissolved in the blood, correct? Would that make any significant difference in exercise endurance?
 
zzyzx said:
Wow, thanks for all the quick replies!

So, in a healthy person, how would this very high PaO2 affect the amount of oxygen actually available to the tissues? The SpO2 wouldn't change to any significant amount since it's already near 100%, but there would be more oxygen dissolved in the blood, correct? Would that make any significant difference in exercise endurance?
Click to expand...

Insignificantly more. The equation for total oxygen content is:

CaO2 = (SaO2 x Hb x 1.34) + .003(PaO2)

The first term is hemoglobin-bound oxygen (saturation % times hemoglobin concentration times a volume constant), the second term is dissolved oxygen. You can see how the latter is almost negligible -- a couple percent of the total oxygen in blood. If we couldn't attach oxygen onto little hemoglobin busses, we could only transport a fraction of the oxygen needed to sustain life in our blood (at least at plausible atmospheric pressures... maybe in a hyperbaric chamber or something).
 
Brandon Oto said:
Just to check my understanding, this assumes normal body temperature, correct? (-47 is the presumed partial pressure of H2O at said temp?)

Wouldn't this actually yield the PAO2 rather than the PaO2?
Click to expand...

Correct PAO2. Technically there is also anatomic shunting that creates a gradient in the normal patient of less than 10 mmHg from bronchial arteries. When looking at causes of hypoxemia an elevated A-a gradient can give you clues into the issue and how to fix your hypoxemia.

So in the real world actually your PaO2 will be slightly less than your PAO2, unless you got some problems.


Physiology! Fun!
 
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