carbon monoxide

[cage92]

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hey what is the effect of carbon monoxide on o2 binding capacity and saturation? and what is the difference between o2 binding capacity and o2 saturationnnn

 

[seminoma]

Pretty sure there's a thread about this from a few weeks ago.

CO decreases O2 binding capacity and O2 saturation. Capacity is how many the hb can bind. Saturation is how many are actually bound.

 

[Mr. Mojo Risin]

Seminoma answered your question, but here is the link to the other thread for your reference: http://forums.studentdoctor.net/thr...t-shift-in-oxygen-dissociation-curve.1101017/

 

[Mad Jack]

Just remember that clinically, your patient will have an apparent SpO2 that is substantially higher, as CO makes hemoglobin appear saturated.

 

[Mr. Mojo Risin]

Just remember that clinically, your patient will have an apparent SpO2 that is substantially higher, as CO makes hemoglobin appear saturated.

I believe that has more to do with the calculation of SaO2 by a standard pulse oximeter because they do not take into account other forms of hemoglobin (methemoglobin and carboxyhemoglobin). Despite the presence of methemoglobinemia or carboxyhemoglobin, the standard pulse oximeter would give a falsely high reading. If you measure SaO2 with a co-oximeter, the greater number of wavelengths emitted gives you the ability to detect the other hemoglobins for a more accurate reading (in the case of metHb or carboxyHb: decreased SaO2).

 

[cage92]

thank you guys

 

[Mad Jack]

I believe that has more to do with the calculation of SaO2 by a standard pulse oximeter because they do not take into account other forms of hemoglobin (methemoglobin and carboxyhemoglobin). Despite the presence of methemoglobinemia or carboxyhemoglobin, the standard pulse oximeter would give a falsely high reading. If you measure SaO2 with a co-oximeter, the greater number of wavelengths emitted gives you the ability to detect the other hemoglobins for a more accurate reading (in the case of metHb or carboxyHb: decreased SaO2).

This is exactly what I was saying, I just didn't care to explain. It's a very serious thing to keep in mind if you end up with certain cases.

 

[Macaroon_Berry]

Just remember that clinically, your patient will have an apparent SpO2 that is substantially higher, as CO makes hemoglobin appear saturated.

Yes, this is right. You'd have normal O2 Saturation, but the O2 binding capacity would be decreased. That's why I believe you'd look for P50 rather than the O2 sat in CO poisoning.

 

[seminoma]

I believe that has more to do with the calculation of SaO2 by a standard pulse oximeter because they do not take into account other forms of hemoglobin (methemoglobin and carboxyhemoglobin). Despite the presence of methemoglobinemia or carboxyhemoglobin, the standard pulse oximeter would give a falsely high reading. If you measure SaO2 with a co-oximeter, the greater number of wavelengths emitted gives you the ability to detect the other hemoglobins for a more accurate reading (in the case of metHb or carboxyHb: decreased SaO2).

Agreed. pulse-ox in a CO poisoning is normal or "falsely elevated". Some sources (Robbins Review included) don't make a distinction between pulse-ox and co-ox though. I remember doing a question in Robbins that says the pulse-oximetry showed reduced SaO2. The rest of the vignette (and the answer choices) were clearly testing CO poisoning though.

 

[Jabbed]

One important point is that CO binding to Hgb actually shifts the O2 dissociation curve to the left (i.e. increasing oxygen affinity for hemoglobin) which decreases the amount of oxygen that dissociates from hemoglobin to the peripheral circulation.

So all in all, CO competes for the binding sites and decreases the amount of O2 carried by hemoglobin while simultaneously causing the Hgb to hold onto the few oxygen molecules that it does carry even more tightly, thus hampering tissue oxygenation even further.