Hypoxia and Hypoxemia – Not the Same Thing!

There are some words and phrases that get thrown around a lot in med school, that we all think we know, but we don’t always actually know. Today we’re going to discuss some of those.

Hypoxia and hypoxemic are sometimes seen and used as interchangeable, when really they’re not. Hypoxia specifically refers to a deficiency of oxygen supply to the body. Hypoxemia is specific to the lack of oxygen in the blood. Sure, it sounds similar, but they are quite different.

Hypoxemia can cause hypoxia, however you can have an adequate amount of oxygen in the blood, but still have disrupted delivery to the tissue. An example of this may be hemoglobin dysfunction. The RBCs may be carring an appropriate level of oxygen, but they aren’t offloading them at the tissue for some reason.

What about ischemia? Blood can be good, but if something is happening where there is restricted blood flow, say atherosclerosis or hypovolemia, you still have hypoxia. There is not an adequate amount of oxygen delivery to the tissue.

In this way, hypoxia can, of course be local, where you don’t really see localized hypoxemia. I did some extra research on this to be sure, and I wasn’t able to find any clearcut examples of it.

Of course, the signs and symptoms of hypoxia and hypoxemia may be similar since the effect is similar. That’s why its so important to understand the underlying difference. To lump them together is along the same lines of thinking that any patient who presents with pneumonia can be treated in the same way. There is a specific underlying issue that is causing hypoxia or hypoxemia and that is what we aim to treat.

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