avishkar1984
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in CO poisoning the Hb-O2 diss curve shifts to the left
then how dz the arterial PO2 remain normal?
arent the 2 points contradictory?
kaplan notes state that arterial PO2 is a function of dissolved oxygen in the blood.
also then
in cases which cause the curve to shift to the left(decrease pH,etc) the arterial PO2 shd remain normal??
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| new_n_lost
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Hb-O2 diss curve reflects the affinity of Hb to O2 in blood u know wht factors will cause left shift n wht will cause a right shift
Ur question is that in CO poisoning wht happens to Arterial PO2 right??
Well in CO poisoning the Saturation of O2 with Hemoglobin will obviously decrease but as u have said the Kaplan notes mentions a V. Imp point the PaO2 in arterial blood is dictated by Dissolved O2. Therefore since there is relatively no change in Dissolved O2 conc why wud there be a dec in PaO2.
Rmember the Most IMP Points
Anemia = Dec. Hb conc. => Normal PaO2 & SaO2
Methemoglobinemia = Hb Iron gets converted from Ferrous to Ferric forms MetHb( Fe2+ => Fe3+) the Ferric FOrm of Iron cannot Bind to O2 properly thus => Dec. SaO2 & Normal PaO2
CO Poisoning = CO completes with O2 for its binding sites n therefore O2 gets displaced hence it will dec the SaO2 but again the PaO2 is still going to be normal.
Hope u understand these r twisting concepts which we all often confuse.
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| doc179
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PaO2 is the amount of oxygen dissolved in the plasma, as long as the ventillation and the exchange of gases in the lungs are normal PaO2 will always remain normal. Since CO does not affect ventillation and diffusion in the lung PaO2 stays normal.
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| new_n_lost
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Any Change in Ventilation as in Hyperventilation n Hypoventilation or in response to the initial event ( such as Metabolic Acidosis or Alkalosis) will affect the Conc of O2 on BLOOD but unless there is a marked dec in O2 concerntration the Dissolved O2 will not drop.
Edited by new_n_lost on 04/08/07 - 11:33 PM
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| Luckyall
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Actually any HyperVentilation/ supplementing inspired air with O2 in a NORMAL person will increase PaO2 wich is PO2 wich is dissolved O2 with very little effects on Total O2 content ( Total O2 content= O2 attached to Hbg + O2 disolved in plasma), so thas why PO2 is Normal in CO poisoning ( ventilation is Normal since the patient is back in room air---> hence PO2 = dissolved O2= PaO2 is Normal)
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| epica
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Blood Po2 tends to remain normal, because Po2 measurement usually reflects O2 dissolved in blood, not that BOUND to hemoglobin.
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| new_n_lost
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Yes Epica i noticed my mistake n Corrected it
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| epica
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| new_n_lost
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thanks for Correcting me. A buddy of mine also noticed the same thing informed me at the same time
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| epica
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We are in the same boat...
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| avishkar1984
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thanks a lot guys
i hv finally got the concept
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