Cyanide poisoning O2 labs

[Transformers]

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Cyanide toxicity confuses me...wouldn't you get normal O2 labs (PaO2, SaO2)? afterall cyanide just hits the complex IV of the ETC not really anything relating to O2 other than the fact that the intracellular O2 won't be able to accept the elctrons...

as far as the LINK to methemoglobinemia, cyanide doesnt cause it (nitrites induce the Fe3+ form right...which has a greater affinity for cyanide but that doesn't mean its a trigger)

Hence if you had two scenarios:
1.) Nitrite ingestion alone (hence methemoglobinemia)
2.) Cyanide ingestion alone

Essentially O2 sats (and total O2) would be down in Nitrite ingestion right but should be normal with cyanide ingestion am i correct?

 

[VCorp]

Your post just gave me the biggest headache possible, so I'll just give you the simple gist of what happens. Meth-Hb basically have Fe3+ compared to 2+, this won't bind to oxygen. Since it doesn't bind to oxygen, SaO2 will be decreased, but PaO2 will be normal. Normal, because there is no problem getting oxygen across the alveoli and to be able to be dissolved in the plasma. SaO2 is measuring "saturation" how much oxygen is bound to hemoglobin. In Fe3+ state, oxygen can't bind to hemoglobin, so the saturation rate will be low.

 

[loveoforganic2]

Your post just gave me the biggest headache possible, so I'll just give you the simple gist of what happens. Meth-Hb basically have Fe3+ compared to 2+, this won't bind to oxygen. Since it doesn't bind to oxygen, SaO2 will be decreased, but PaO2 will be normal. Normal, because there is no problem getting oxygen across the alveoli and to be able to be dissolved in the plasma. SaO2 is measuring "saturation" how much oxygen is bound to hemoglobin. In Fe3+ state, oxygen can't bind to hemoglobin, so the saturation rate will be low.

Well I hope your house has a carbon monoxide detector

 

[Transformers]

your answer didn't answer my question...you just described what O2sats was...im asking that in terms of cyanide vs. nitrites

 

[athadam]

I think SaO2 would increase in cyanide poisoning since cells are unable to utilize O2 thus more O2 would remain bound to hemoglobin.

 

[HoboCommander]

In cyanide poisoning, SaO2 is normal, says right on Goljan RR 4th page 15.

 

[loveoforganic2]

In cyanide poisoning, SaO2 is normal, says right on Goljan RR 4th page 15.

Venous SaO2 will for sure be increased. My guess would have been that arterial SaO2 would be slightly decreased (some CN will complex w/heme iron in hemoglobin)

 

[HoboCommander]

Yes I agree, venous SaO2 would be increased. This can in turn increase arterial SaO2 (I think this would be a stronger factor than the mechanism of decrease you mention), which would still be normal SaO2. Whatever the case, on the test you would say it is normal because it is generally accepted knowledge and SaO2 is very easy to measure in the real world.

 

[Transformers]

thanks...yeah im just not too sure about the idea of "O2 sats increasing" in cyanide toxicity...i mean the key question you ask yourself regarding O2 sats measurement for ANY disorder is can each RBC bind to 4O2 (i.e.- in the case of methemeglobinemia and CO poisoning...the answer is no so O2 sats drop)