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Old 08-25-2011
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Question PAco2 and PaCO2, any difference in alveolar gas equation?

Ok this has been bugging me for a while now...

In the alveolar gas equation what value is used in the calculation, alveolar CO2 or arterial CO2?

I've checked numerous sources online, and some say one thing and others indicate different.

I've checked with Costanzo's Physiology book, and she uses alveolar CO2 similar to First Aid 2010...HOWEVER...according to FIRST AID ERRATA:

"508 Alveolar gas equation
In three instances, in the abbreviation for arterial carbon dioxide
pressure, change the capital A to a lower case a, to indicate we‟re
measuring arterial carbon dioxide pressure instead of Alveolar. "

I'm probably looking too much into this, but it really is driving me crazy!

Thanks in advance lol
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Old 08-26-2011
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Ok, let me try to explain you

When we inspire air, it has PCo2 = 0. -->

Air reaches alveoli, now PACo2 (alveolar) = 40. -->

This is mix up with the pul blood and now pul blood have PaCo2 = 40 same as alveoli. -->

This blood goes to tissue where CO2 is formed and CO2 diffuses back to this blood raising this blood conc. from 40 to 46(because of CO2 from tissues). so PaCO2 = 46 -->

Now, this goes back to pul capillaries and to alveoli and it now changes from 46 to 40. This is how it keeps on going.

Hope it is bit clear now
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