Hypoxemia vs. Hypoxia

[leviathan]

I was talking with an internist about the differences between these two terms, and I'm not sure I believe his answer. I figured you guys would be the experts on this, so here goes:

His definition:
Hypoxemia = PO2 < 100 (decreased plasma O2 concentration)
Hypoxia = SaO2 < 95%


My definition:
Hypoxemia = Decreased CaO2 (Hb, SpO2, Plasma [O2])
Hypoxia = Decreased DO2 (Decrease in CaO2, Cardiac Output, or SaO2-SvO2)

Who is right? Or are we both wrong?

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[urge]

Posted via Mobile DeviceI think you are wrong. Too far fetched for my taste.

Hypoxia and hypoxemia is the same in my book. Lower o2 than expected.

 

[Trisomy13]

I consider hypoxemia, by definition, to be PaO2 < 60.

And hypoxia a term used to describe low blood oxygen content, but not always necessarily such that it results in hypoxemia.

I forget exactly how Miller or M&M defines hypoxia, but it's technically different than hypoxemia.

 

[leviathan]

I consider hypoxemia, by definition, to be PaO2 < 60.

And hypoxia a term used to describe low blood oxygen content, but not always necessarily such that it results in hypoxemia.

I forget exactly how Miller or M&M defines hypoxia, but it's technically different than hypoxemia.

Hmm...interesting. Sounds like you are leaning towards my friend being right. To me, the word itself seems to refer to the CaO2. So if you are anemic, you would be hypoxemic, even with a normal PO2. But I guess not?

 

[urge]

Posted via Mobile Device
What's the difference between hypercarbia and hypercarbemia?

 

[InductionAgent]

I was talking with an internist about the differences between these two terms, and I'm not sure I believe his answer. I figured you guys would be the experts on this, so here goes:

His definition:
Hypoxemia = PO2 < 100 (decreased plasma O2 concentration)
Hypoxia = SaO2 < 95%


My definition:
Hypoxemia = Decreased CaO2 (Hb, SpO2, Plasma [O2])
Hypoxia = Decreased DO2 (Decrease in CaO2, Cardiac Output, or SaO2-SvO2)

Who is right? Or are we both wrong?

Hypoxemia refers specifically to low oxygen content in the blood (hence the -emia).

Stedman's definition of hypoxemia: "subnormal oxygenation of arterial blood, short of anoxia"

Hypoxia is a less specific term, refering to low oxygen content in any tissue, including blood.

Stedman's again for hypoxia: "decrease below normal levels of oxygen in inspired gases, arterial blood, or tissue, short of anoxia"

The distinction is subtle but sometimes relevant in that changes in blood oxygenation and end-organ oxygenation will sometimes be staggered from one another. For instance, end-organ hypoxia will lag slightly behind the development of hypoxemia. Transient episodes of hypoxemia do not always result in clinically significant hypoxic episodes.

 

[leviathan]

Hypoxemia refers specifically to low oxygen content in the blood (hence the -emia).

Stedman's definition of hypoxemia: "subnormal oxygenation of arterial blood, short of anoxia"

Hypoxia is a less specific term, refering to low oxygen content in any tissue, including blood.

Stedman's again for hypoxia: "decrease below normal levels of oxygen in inspired gases, arterial blood, or tissue, short of anoxia"

The distinction is subtle but sometimes relevant in that changes in blood oxygenation and end-organ oxygenation will sometimes be staggered from one another. For instance, end-organ hypoxia will lag slightly behind the development of hypoxemia. Transient episodes of hypoxemia do not always result in clinically significant hypoxic episodes.

Nice, thank you for that. So hypoxia is definitely the same definition I gave for it (decreased tissue O2 delivery).

But when they say "subnormal oxygenation of arterial blood, short of anoxia", are they just referring to the PO2 and dissolved content, or also the hemoglobin concentration and saturation?

 

[Trisomy13]

Hmm...interesting. Sounds like you are leaning towards my friend being right. To me, the word itself seems to refer to the CaO2. So if you are anemic, you would be hypoxemic, even with a normal PO2. But I guess not?

no, by those definitions, if you are anemic, you could be hypoxic, but have a normal PaO2 and not be hypoxemic.

again.. hypoxia is more of a vague term, not defined by a value, whereas hypoxemia, according to M&M anyway, is PaO2 < 60.

 

[fakin' the funk]

again.. hypoxia is more of a vague term, not defined by a value, whereas hypoxemia, according to M&M anyway, is PaO2 < 60.

Yep.

Would you believe that I dug out Harrison's to answer this question and IT WASN'T IN THERE? Not surprised at all, really. Back to being a paperweight.

 

[Planktonmd]

To put it in simple terms:
Hypoxia: Patient not getting enough oxygen which could be because of low oxygen in inspired gases or something preventing oxygen from reaching the patient including lung disease.
Hypoxemia: Not enough oxygen in the blood regardless of the etiology.
Hypoxemia is the result of hypoxia on the level of blood.

 

[leagueelbow]

I was told hypoxemia is low O2 content in tissues.

Hypoxia is the after effects. i.e. You're really in trouble when hypoxia occurs as a result of prolonged hypoxemia.

 

[deleted9493]

Esa no es verdad.

I was told hypoxemia is low O2 content in tissues.

Hypoxia is the after effects. i.e. You're really in trouble when hypoxia occurs as a result of prolonged hypoxemia.

 

[amyl]

I was told hypoxemia is low O2 content in tissues.

Hypoxia is the after effects. i.e. You're really in trouble when hypoxia occurs as a result of prolonged hypoxemia.

i have always thought of hypoxemia as refering to blood (not enough O2 in blood), and hypoxia as inadequate oxygenation at the tissue level.

 

[Trisomy13]

lest we ever forget the anesthesiologist's capacity to debate the known and mundane.

 

[DrDre311]

You guys should have posted this in the ortho forum.

 

[InsatiableId]

Hypoxemia = Decreased oxygen in the blood.

Hypoxia = Decreased oxygen.


Both of these are relative terms, so their definitions in medicine are somewhat arbitrary... it really depends on what you're comparing to.

Most people would define hypoxia as the threshold of tissue oxygenation below which measurable end organ damage occurs. As far as I know, there is no good single direct measurment of oxygen that would define hypoxia, you'd actually need to measure values that indicate damage to a given organ.

With hypoxemia, most sources would probably define it as PaO2 < 60 mm Hg, as that is an average level of dissolved plasma oxygen at which hypoxia occurs. In my opinion, a better definition, and one that is more directly related to hypoxia, would use CaO2, as you'd mentioned.

In a clinical setting, I would say you should take into acount both CaO2 and any factors that would shift the oxyhemoglobin dissociation curve (thus affecting the amount of oxygen the tissue can utilize).

How's that for semantics? Oh, and please do a physical exam (frankly, I'm tired of reading chest and abdominal CT's on call for clinicians that can't do an appropriate exam... although I guess I'll be appreciative once I get paid for reading them).

 

[jetproppilot]

you Guys Should Have Posted This In The Ortho Forum.

hahahahahahahahahahahahaha

 

[Strength&Speed]

eh, never mind

 

[leviathan]

eh, never mind

Too late, my auto email told me what you originally wrote! We don't want you here anyway, go back to ortho!

 

[leviathan]

With hypoxemia, most sources would probably define it as PaO2 < 60 mm Hg, as that is an average level of dissolved plasma oxygen at which hypoxia occurs. In my opinion, a better definition, and one that is more directly related to hypoxia, would use CaO2, as you'd mentioned.

Hell yes. It's misleading to insinuate that low blood oxygen content (translation of hypoxemia) is solely determined by PO2. I guess my buddy is right though, but being pedantic I still argue it was a draw.

 

[Bougie]

i have always thought of hypoxemia as refering to blood (not enough O2 in blood), and hypoxia as inadequate oxygenation at the tissue level.

I agree with this.

You can have plenty of oxygen in the blood and still have an organ/tissue that is hypoxic for whatever reason (i.e. sepsis).

 

[Leverage]

Hell yes. It's misleading to insinuate that low blood oxygen content (translation of hypoxemia) is solely determined by PO2. I guess my buddy is right though, but being pedantic I still argue it was a draw.

Exactly... A PaO2, dissolved O2, that gets halfed ( 90 to 45) will drop your total CaO2 from 200 to 163 in a normal person. If you half someones Hgb (15 to 7.5 ) will drop your total CaO2 from 200 to 101. Hypoxemia (paO2) is good for ABGs and finding out what going on in the lungs, but tells you almost nothing of total CaO2 in the blood.

 

[Duane E]

I agree with this.

You can have plenty of oxygen in the blood and still have an organ/tissue that is hypoxic for whatever reason (i.e. sepsis).

True dat! I suppose cyanide poisoning would also be an example. If we go with PaO2<60 as the definition of hypoxemia, then methemaglobinemia would be another.
Check those Lactic acid levels!