hemoglobin saturation

[jfgavina]

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when it is bound to CO will it appear saturated in the oxymeter?

 

[MrBeauregard]

No. Standard pulse oximetry will only measure oxyhemoglobin (that with O2 bound) and deoxyhemoglobin (that without O2 bound). It will not pick up on what are called dyshemoglobins; these are methemoglobin (reduced, or ferric [Fe3+], hemoglobin) and carboxyhemoglobin (hemoglobin with CO bound). Dyshemoglobins shift the O2-dissociation curve to the left, thus increasing the affinity of hemoglobin for oxygen and decreasing O2 delivery to tissues.

The inability of standard oximetry to measure dyshemoglobins can be a problem because a person may be put on an oximeter and the SaO2 measures at 97% when, in reality, this percentage is incorrect because the oximeter can only measure oxyhemoglobin, which would be the 97%. The patient may have increased amounts of methemoglobin or carboxyhemoglobin which can cause a multitude of problems, the most obvious of which is hypoxia leading to seizures, coma and death.

To remedy this problem, we use co-oximetry, which emits light at various wavelengths in order to measure oxy-, deoxy-, met- and carboxyhemoglobin.

 

[Chirurg]

Yes, the reading will show you a full saturation neglecting that now half of your hemoglobin is actually useless. The above poster explained it very well.

 

[jfgavina]

ok I got it thank you both. but for step 1 purposes CO and Methemoglobinemia decrease saturation and increase hemoglobin affinity for oxygen right?

 

[islandCrazy]

I would also like to say thanks for that explanation because it was something I thought I knew but clearly was completely off about.

 

[MrBeauregard]

ok I got it thank you both. but for step 1 purposes CO and Methemoglobinemia decrease saturation and increase hemoglobin affinity for oxygen right?

Yes, carboxyhemoglobin and methemoglobin decrease the true oxygen saturation. And yes, they both shift the curve to the left.

I would also like to say thanks for that explanation because it was something I thought I knew but clearly was completely off about.

You're welcome.

 

[gravitywave]

I would also like to say thanks for that explanation because it was something I thought I knew but clearly was completely off about.

me too. thanks MrB