phuluong2k
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Why it has normal Pa02 on ABG & low PaO2 on pulse oxymetry
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| alenka
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in metgemoglobinemia:
1-PaO2 which is the partial pressure of oxygen=the amount of oxygen dissolved in plasma is normal because there's nothing that stops O2 from getting to your blood.
2-SaO2 which is the oxygen saturation=the oxygen bound to your hemoglobin is decreased because the iron is +3 instead of +2 and cannot bind the oxygen.
and since the pulse oxymeter measures your PaO2 level-it will be normal.and ABG should be NO different.and of course SaO2 will be low,which makes total blood oxygen low.
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| Renegade
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Actually, it seems that your average ABG sample (SaO2) takes into account ALL hemoglobins, including carboxy/methemoglobin (relating them to oxyhemoglobin), while pulse oximetry (SpO2) only relates «oxyhemoglobin» to reduced hemoglobin. This «oxyhemoglobin» includes methemoglobin (and carboxy) because their wavelengths are quite similar...
If there is circulating methemoglobin, oxyhemoglobin will falsely increase (it'll be oxy + methe instead), so it's ratio with reduced hemoglobin will increase in arterial blood -> hence the «false superior» value for SpO2. Interestingly, the opposite effect can be obtained by messing with wavelengths in unexpected ways... consider nailpolish!
Note: Can you find the mistake in this article's section on pulse oximetry?
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| phuluong2k
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Thanks, i type wrongly, it is a low Sa02 on pulse oxymetry
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