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Old 04-22-2012
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Blood O2 content is normal or decreases in anemia?

let's say you have fibroids, and therefore bleeding, what will be the changes to O2 content, O2 saturation and arterial PO2?



These kinds of questions have troubled me for months so please explain your answer. Some things change and some stay normal, but I've never understood why.

Thanks in advance.
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Old 04-22-2012
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pO2 is just the O2 that gone to the blood from the lungs by diffusion, it is normal in anemia. Anemia is the lack of RBC's so the amount of hemoglobin is also dicreased (a protein within RBC that binds O2) so the HB is decreased. But the O2 saturation is normal, because the hemoglobin that is still in there binds O2 normaly.

Conclusion: in Anemia O2 saturation is normal, pO2 is normal, but HB is decreased.

Oxygen content:
CaO2 = Hb (gm/dl) x 1.34 ml O2/gm Hb x SaO2 + PaO2 x (.003 ml O2/mm Hg/dl)



Oxygen content will be decreased due to decrease in HB
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Yeah, I agree. The O2 saturation would be normal.

But if you have less Hb to bind to the O2 then PaO2 (O2 content) would decrease as well ?




...Nvmnd, you edited that post and answered my question at the same time I was typing it out. haha Thanks.

Last edited by Hope2Pass; 04-22-2012 at 04:04 PM. Reason: lol you edited that post and answered my question at the same time I was typing it out.
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Here is the formula
O2 content = (O2 binding capacity x %sat) + PaO2
O2 content is the total oxygen carried by blood so Whatever decreases any one of this values will decrease O2 content
Oxygen binding capacity correlates with Hb concentration (decreased in anemia)
%sat is the the number of heme groups occupied by O2 (decreased in co, methemoglobinemia,) factors that ocupy O2 places on hemoglobin do not affect PaO2 and it is usually norm
And finaly Pao2 is the dissolved ogygen in plasma (as a rule when it is decreased saturation should be low too therefore isolated decrease is not seen)
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Last edited by MedicalExaminer; 04-22-2012 at 04:32 PM.
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Old 04-22-2012
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i think i have an incorrect understanding of what each of those measures mean.

this is what i'm thinking:

PaO2: the pressure of oxygen in the arteries. so how much oxygen is in the arteries (because more oxygen in the blood would increase the pressure of O2 in the blood). So in hypoxemia, decreased PaO2 and in umm, say going from high to low altitude, increased PaO2. Anemia is loss of the Hb so there still would be same O2 in blood, it just cannot bind, so regardless the PaO2 remains normal.

O2 content: ummm i guess i dont really understand what this means, it sounds like what i described above. So maybe its that and my understanding of PaO2 is wrong :/

O2 saturation: sounds like the oxygen that is bound to Hb. so in a problem with Hb, you would have a decrease in O2 saturation but in an anemia due to blood loss, as described in the question, the amount that is bound is still proportionally the same?


help!
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Total o2 content in blood equals (Hb-bound o2, which depends on saturation) + (Dissolved o2 in blood, which is po2)

That's why:
1- Saturation is decreased when u have a quality problem with ur Hb (sush as methemoglobinemia or carboxyhemoglobinemia)
2- Dissolved o2 (or po2) is decreased when ur lungs can't pull oxygen from the air to ur blood (diseases of COPD and restrictive)
3- If there is a decrease in any of the former two, there will be a decrease in total o2 content!

Hope this helps!

P.S. anemia causes decreased o2 total content due to a decrease in the number of Hb (so a single Hb has no problem with the percentage of o2 saturation, it's just that the numbers of Hb are down so the total o2 content is down).
So anemia: normal saturation, normal po2, decreased total o2 content

Last edited by Renaissance; 04-22-2012 at 04:51 PM.
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Anemia does not affect saturation

PaO2 is just dissolved oxygen in plasma whereas a correct term for total oxygen carried by blood is oxygen content
When person living on high altitude descends to low - he increases oxygen content due to following factors: he has increased oxygen binding capacity (polycythemia) and increase in saturation of Hb and PaO2 due to increased partial pressure of oxygen (due to increase in Atmospheric pressure)
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In ur question above
Bleeding decreases Hb leaving unaffected saturation and PaO2
And there is decrease in ofygen content of blood (which is total oxygen bound and dissolved)
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Old 04-23-2012
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ok so in bleeding,

the PaO2 is normal (proportional loss of dissolved O2 in blood and loss of blood itself), O2 content is decreased (loss of blood and O2), and O2 saturation is normal?

is this right?
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Bleeding ---> anemia:
-Decreased total o2 content in blood
-Normal saturation
-Normal po2


Just to sum everything up:
Total o2 content in blood = dissolved o2 + Hb-bound o2

Therefore, the total o2 content depends on three things:
Dissolved o2
1-po2

Hb-bound o2
2- Hb saturation
3- Hb concentration
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ok i think i got it!

thanks guys!
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Quote:
Originally Posted by Dr.NickRiviera View Post
ok i think i got it!

thanks guys!
i will still suggest you first audio lecture of goljan of respiratory
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Quote:
Originally Posted by Kabutar111 View Post
i will still suggest you first audio lecture of goljan of respiratory
haha yea i think i might have to
thanks!
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Quote:
Originally Posted by Dr.NickRiviera View Post
haha yea i think i might have to
thanks!
welcome
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Quote:
Originally Posted by MedicalExaminer View Post
Here is the formula
O2 content = (O2 binding capacity x %sat) + PaO2
O2 content is the total oxygen carried by blood so Whatever decreases any one of this values will decrease O2 content
Oxygen binding capacity correlates with Hb concentration (decreased in anemia)
%sat is the the number of heme groups occupied by O2 (decreased in co, methemoglobinemia,) factors that ocupy O2 places on hemoglobin do not affect PaO2 and it is usually norm
And finaly Pao2 is the dissolved ogygen in plasma (as a rule when it is decreased saturation should be low too therefore isolated decrease is not seen)
Help interpret

ph 7.38
pCO2 45
pO2 81
Oxygen saturation 99
Bicarbonate 26
Hemoglobin 12.5
FIO2 21

Thanks
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