Cyanosis with a High SpO2?

[BEorP]

I've been wondering about a question that came up in the podcast thread but didn't want to hijack that thread to bring it up again. There a comment was made that you would never want to be that medic who denies a cyanotic patient oxygen because they have a high SpO2.

What I am wondering is if there is a time that this would happen aside from a problem with the SpO2 reading.

Patients with anemia may never become cyanotic because they cannot have a high enough concentration of deoxygenated Hb in their blood to display the blue colour, but that is the reverse of what we're talking about. The other extreme is patients with polycythemia who could have cyanosis under normal conditions since they have so much available Hb that it may not all be saturated, but this would show a low SpO2.

Any thoughts?

 

[HotelCo]

Carbon monoxide.

 

[TransportJockey]

'CO Can and will do this. Cherry red is usually a late or post mortem sign. Pts with CO exposure might show 100% on the sat monitor (which at my altitude would be unusual without low flow o2)

 

[BEorP]

Thanks for your comments, but do you happen to have a source for that? I have never read that CO poisoning is associated with cyanosis (for example Rosen's Emergency Medicine, 7th Edition says that "Carbon monoxide and cyanide poisoning do not typically present with cyanosis"). This would make sense since the blue in cyanosis is due to the deoxyhemoglobin, which isn't what the problem is in CO poisoning since the CO is bound to the Hb.

 

[Death_By_Sexy]

A high SpO2 could be due to any number of reasons. Even the CO angle isn't it solely, there's a reason pulse oximetry is always secondary to proper assessment.

 

[BEorP]

A high SpO2 could be due to any number of reasons. Even the CO angle isn't it solely, there's a reason pulse oximetry is always secondary to proper assessment.

I guess this is sort of why I started the thread. MedicRob had made a comment in the podcast thread that you would never want to deny someone oxygen who is cyanotic based on the reasoning that their SpO2 is fine. I've heard this line previously and never really stopped to think about it. Now that I have, I can't think a clinical condition where someone would have a cyanosis with a good SpO2 reading. If you can think of one though I would love to hear it.

I don't entirely agree with the idea that pulse oximetry is "secondary". Especially with the 2010 ECC guidelines, SpO2 really is an important assessment that will be important in guiding treatment (with O2 not being used for ACS patients with high SpO2 on room air).

 

[Journey]

Methemoglobinemia

Look up all the things associated with it.

 

[Smash]

SpO2 isn't really measuring oxygen saturations. It's just a redness meter really, and all it measures is bound and unbound hemoglobin by their different wavelengths. Most pulse oximeters deal with only two things: oxyhemoglobin and deoxyhemoglobin. So anything that is bound to hemoglobin such as cyanide or carbon monoxide will make the monitor think it is dealing with oxyhemoglobin.


I could be wrong but I believe that methemoglobinemia will indeed present with cyanosis, but it will also have low SpO2 readings, in some cases extremely low. However I think that it still overestimates actual PaO2, so the caveat still remains: if patient is blue, ignore SpO2. Well maybe no ignore, but that is kind of catchy.

I'll have to wait till I get home from holidays to check my trusty old Goldfranks Toxicologic Emergencies.

 

[BEorP]

Methemoglobinemia

Look up all the things associated with it.

Good thinking! That is probably as close as we can get in finding something that presents with cyanosis and a high SpO2. Apparently with traditional pulse oximetry there is often an unreliable low reading in patients with mild methemoglobinemia and an unreliable high reading in patients with high-level methemoglobinemia.

For anyone who wants to read more about it:
http://emedicine.medscape.com/article/815613-workup

Thanks a lot for the response, Journey.

 

[BEorP]

SpO2 isn't really measuring oxygen saturations. It's just a redness meter really, and all it measures is bound and unbound hemoglobin by their different wavelengths. Most pulse oximeters deal with only two things: oxyhemoglobin and deoxyhemoglobin. So anything that is bound to hemoglobin such as cyanide or carbon monoxide will make the monitor think it is dealing with oxyhemoglobin.


I could be wrong but I believe that methemoglobinemia will indeed present with cyanosis, but it will also have low SpO2 readings, in some cases extremely low. However I think that it still overestimates actual PaO2, so the caveat still remains: if patient is blue, ignore SpO2. Well maybe no ignore, but that is kind of catchy.

I'll have to wait till I get home from holidays to check my trusty old Goldfranks Toxicologic Emergencies.

That is awfully catchy! It is still good to have a discussion like this to understand why we're giving O2 to anyone who is blue regardless of SpO2. I had also heard before that methemoglobinemia would present with a low SpO2 reading, but it looks like there is a bit more to it than that (at least according to the Medscape link that I posted above). I guess it is actually sometimes high and sometimes low, depending on how bad it is.

 

[Sandog]

There can be other issues that can give a false high SPO2 while the patients symptoms and visual signs would indicate quite the contrary. For example; the unit might be broken? Sometimes in the field, the look, listen, feel technology beats the high technology.

 

[HotelCo]

^ especially if you have a zoll monitor. Those things are a piece of junk, especially the SpO2

 

[Smash]

^ especially if you have a zoll monitor. Those things are a piece of junk, especially the SpO2

Or a Philips MRx, enormous steaming pile of turds that they are.

 

[BEorP]

There can be other issues that can give a false high SPO2 while the patients symptoms and visual signs would indicate quite the contrary. For example; the unit might be broken? Sometimes in the field, the look, listen, feel technology beats the high technology.

Hopefully if there is technical problem with getting the reading there would be a poor waveform at least to suggest that it may not be the most reliable... though I think usually on the Zolls that requires going into manual mode for some strange reason.