Step I hemoglobin saturation

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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.
 
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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.
 
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ok I got it thank you both. but for step 1 purposes CO and Methemoglobinemia decrease saturation and increase hemoglobin affinity for oxygen right?
 
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jfgavina said:
ok I got it thank you both. but for step 1 purposes CO and Methemoglobinemia decrease saturation and increase hemoglobin affinity for oxygen right?
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Yes, carboxyhemoglobin and methemoglobin decrease the true oxygen saturation. And yes, they both shift the curve to the left.

islandCrazy said:
I would also like to say thanks for that explanation because it was something I thought I knew but clearly was completely off about.
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You're welcome.
 
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