Blood gases

Discussion in 'Medical Students - MD' started by Mossjoh, Jun 21, 2002.

  1. Mossjoh

    Mossjoh Mayo Clinic-PGY2
    10+ Year Member

    Jan 1, 2001
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    Okay...just a quick question.

    The Henderson-Hasselbalch equation states that

    pH = pKa + log ([HCO3-]/(0.3)(pCO2))

    Now..if the question states...

    "After a period of insulin treatment, the man's blood pH returns to normal (7.4) and the [HCO3-] = 21mM. Calculate the Total CO2 content in the blood.

    Well, since 95% of the CO2 in the blood travels as bicarbonate, wouldn't you just take the 21mM as that 95% and then multiply by 1.05 to get 100%, which would be 22mM as the total CO2 content? Is another calculation needed?

  2. beezar

    beezar Senior Member
    7+ Year Member

    Jan 31, 2002
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    Hmm, from what I remember reading, there is no good formula to calculate total CO2 content in blood (read it in the ICU book) because of the complex interaction of bicarb/co2 with RBCs (Hemoglobin binds the H+ that comes off when H2CO3 dissociates). But don't quote me on this!

    Anyway, if you did use the 95% principle, you would divide by 0.95 rather than multiplying by 1.05 (which would give you almost the same number anyway...

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