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Discussion

CCRN Study: So confused on dead space vs. shunt

Is COPD considered dead space or shunting? I understand that dead space is ventilation without perfusion and examples include lack of blood flow to the lungs, pulmonary embolism, since the aveoli is getting air but there is a problem with circulation to the lungs.

Shunting is good perfusion, but bad ventilation and this can happen because air is having trouble getting into/through the aveoli for ventilation. I'm thinking this is where COPD lies. Examples I read for this was atelectasis, ARDS, mucus plugs, pneumothorax, and pleural effeusions.

Am I on the right track? Thanks :)

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    Here's one way to think about this....

    A rise in dead space will result in a rise in PaCO2

    A rise in shunt flow will result in a fall in PaO2 and therefore SaO2.

    So, in the over simplified patient in the CCRN exam, COPD might result in retention of CO2 because of how much dead space is developing because of the disease.

    But...in real life, patients are sicker and have both shunting (fall in SaO2) because of mucous plugs, bronchospasm etc. AND increased dead space (rise in CO2) because of alveolar destruction and useless ventilation.

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    Thanks offlabel! That makes it very simple to remember. And you're right, in real life, its a mix of both. I think that's where I get messed up with understanding at times because I try to relate everything I read to the patients I have (especially the sicker ones who have a bunch of issues going on, its hard to pinpoint exactly why they are hypoxemic). Sometimes, I put these patients in the CCRN study box, but I see now that they're much more complex than that.

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