Question about the oxyhemoglobin desaturation curve

Specialties MICU

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Specializes in ICU, oncology.

I am foolishly taking the CCRN exam today and while I get the general concept of the affinity of oxygen and hgb what confuses me are the 2, dpg things. I had written in my notes that 2,3 dpg is what makes the hgb stick to the O2 so would more 2,3,dpg shift the curve to the left? My notes say the opposite, I am just trying to make some sense here. :banghead:.

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Specializes in ICU/ER/TRANSPORT.

This is how I have it just explained to me by our icu resident rrt, and his rationale is what I used for my exam. Here it goes, the curve is shifted to the right by 2,3 dpg and a right shift makes it harder for hemoglobin to bind to o2 but makes it easier to release o2 from the hemoglobin. And a left shift on the curve is just about the opposite. A increase of 2.3 dpg would cause the curve to shift to the right a decrease cause a shift to left.

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Specializes in ICU, oncology.

Thanks for the help bullydawg. I am happy to say I passed the test!

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Specializes in ICU/ER/TRANSPORT.

Well congrats.. Just to be nosey, what material did you use to study with for the exam?

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Specializes in Cardiac.
Well congrats.. Just to be nosey, what material did you use to study with for the exam?

I'd like to know too!

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Specializes in ECMO.

an INCREASE in 2,3 DPG decreases the affinity of O2 to Hb and so O2 will be more readily released at the tissues = RIGHT SHIFT. this helps to explain why a patient may be HYPOXEMIC yet NOT HYPOXIC.

this is how i always think of the curve:

draw it out and label the Left and right

LEFT shift is good for the LUNGS

RIGHT shift is good for the tissues.

-what i mean by this is that with a LEFT shift oxygen binding is increased, so the RBCs can pick up "more O2" as they pass the ACM. the bad side to this is that the RBCs do not want to "let go" of the O2 so readily at the tissues.

-with a RIGHT shift oxygen binding is decreased at the lungs so less is picked up by the RBCs, but whatever 02 is picked up is more readily released and available to the tissues for metabolism. so this kind of a compensatory effect.

-any INCREASE in temp, 2,3 DPG, CO2 and HYDROGEN ION concentration (decreased pH) causes a RIGHT shift, (except for increases in carbon monoxide)

-any DECREASE in the above causes a LEFT shift.

-dont forget that normally P50 is at 27mmHg. 50% saturation at 27mmHg, and any PaO2 below 60mmHg (90% Sa02) causes a rapid decline in amount of O2 bound to Hb which decreases O2 delivery to the tissues.

300px-Oxyhaemoglobin_dissociation_curve.png

hope this helps.

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Hi!

May i ask what does ACM mean? I'm trying to figure it and am looking all over the internet, but i don't find an answer.

Thanks

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Specializes in CTICU.

I would guess alveolar capillary membrane based on the post.

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Specializes in ECMO.

correct

sorry about not responding earlier

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Thank you, ghillbert! :wink2:

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Specializes in CTICU.

You're welcome :)

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