Cyanosis

[bbpiano1]

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I was always under the impression that cyanosis was a function of O2 sat, but FA and Wiki claim that a Hb<5 will also produce cyanosis....

"Cyanosis is a blue coloration of the skin and mucous membranes due to the presence of deoxygenated hemoglobin in blood vessels near the skin surface, or a reduction greater than 5 gm% of hemoglobin."

If you had 5 g/dL Hb and maintain good ventilation, wouldn't you just see pallor?

 

[DragonWell]

I was always under the impression that cyanosis was a function of O2 sat, but FA and Wiki claim that a Hb<5 will also produce cyanosis....

"Cyanosis is a blue coloration of the skin and mucous membranes due to the presence of deoxygenated hemoglobin in blood vessels near the skin surface, or a reduction greater than 5 gm% of hemoglobin."

If you had 5 g/dL Hb and maintain good ventilation, wouldn't you just see pallor?

Just a thought, but perhaps if you have less overall hemoglobin, a greater % of it will be deoxygenated by the time it gets to venous blood, thus resulting in cyanosis even with normal ventilation.

Edit: I remembered reading something about this in West's Respiratory Phys - it's on pg 78. He says, "Because it is the amount of reduced Hb that is important, cyanosis is often marked when polycythemia is present but is difficult to detect in anemic patients."

I'm not sure how that resolves with my previous statement...

 

[agranulocytosis]

I always thought cyanosis was defined as the absolute number of reduced (i.e. deoxygenated) hemoglobin molecules being 5 mg/dL or greater. This means that in polycythemia, that 5 gm/dL value will be far easier to reach than in anemia.

 

[Tired Pigeon]

I always thought cyanosis was defined as the absolute number of reduced (i.e. deoxygenated) hemoglobin molecules being 5 mg/dL or greater. This means that in polycythemia, that 5 gm/dL value will be far easier to reach than in anemia.

Yeah, my understanding is at a really low hemoglobin level you can't have a high enough absolute number of deoxygenated Hb to get cyanosis. Your patient can still be in terrible shape, of course, but not, per se, cyanotic.

 

[nowai]

That is also what the quoted text in the OP is saying.... the OP just misread it.