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Old 12-19-2013
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Question Oxygen/methemoglobin, Cyanide, CO and oxygen physiology

Anyone here who can clear up this different pathologies, and how the PaO2, Sat02, Oxygen content, Tissue 02 extraction/ venous 02 return is affected in each pathology, i usually forget these because i mix them up sometimes, so any1 know where i can clear this up?
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Old 12-20-2013
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Originally Posted by Ianmrz View Post
Anyone here who can clear up this different pathologies, and how the PaO2, Sat02, Oxygen content, Tissue 02 extraction/ venous 02 return is affected in each pathology, i usually forget these because i mix them up sometimes, so any1 know where i can clear this up?
There are certain concepts to remember:

1. MetHB (Fe in +3 state): hates O2, doesn't bind to it.

2. COHb (Hb has higher affinity for CO than O2): increases overall affinity of Hb towards O2 (hence the L shift of O2-Hb disso curve) but at the same time decreases the O2 carrying capacity of Hb as it occupies O2's place

3. Cyanide : has higher affinity for MetHb than normal Hb & blocks ETC heme

4. PaO2 is the measure of dissolved O2 in plasma It has nothing to do with Hb or their abnormalities.

5. SaO2 is how much Hb is saturated with O2. If all 4 sites of O2 are occupied, then there's 100% saturation (measured by pulse oximeter pinched on a finger tip). CO decreases this by around half.

6. Oxygen content is O2 bound to Hb plus O2 dissolved in plasma & depends on them both & is affected as above.

7. Tissue O2 extraction really depends on the O2 tension in the tissue & the curve. As the O2 tension in the tissues falls, there's more O2 extraction from Hb as demonstrable from the disso curve. Also the shape of curve (which depends on H+, BPG, temp...) determines how much O2 is to be delivered at a particular tissue O2 pressure. A left shift increases affinity of O2 to Hb & so tissues find it difficult to extract same amount of O2 as was being extracting earlier as per the normal curve. Venous O2 return or Mixed venous O2 content, again, depends on how much the tissue extracts O2 & how much the Hb lets the tissue extract O2 bound to it as per the prevailing affinity seen on curve (increased extraction in exercise & low MVO2).

Hope this helps a bit.
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Old 12-20-2013
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Yea thanks for the reply, i know those concepts but sometimes i freak out on some of the questions and confuse an up or down and arrow and mess it up, just wanted like a compilation for each one individually though
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