View Full Version : Question about Anemia and Hb...very confusing : <

05-26-2006, 03:03 PM
Hey Guys,
Just wondering if I can get some general help.....my question is in cases of anemia, what variables will decrease? I know that O2 capacity will drop for sure b/c it is capacity is directly related to the Hb concentration. How about total O2 content? I know that content is determined by Hb sat + dissolved O2, but dosen't Hb sat is determined by O2 content-dissolved O2 / O2 capacity? I am kinda confused btwn O2 capcity and content, seems related in a sense. Thx in advance.

05-26-2006, 03:48 PM
Hi, Jack !
O2 content is the concentration of O2 in the blood= approx 0.2ml of O2 per ml of arterial blood. ( 20 volumes%) .
total oxygen content= oxygen attached to Hb ( most is found in this form)+ oxygen dissolved in plasma( very little).
In anemia, the concentration of Hb is decreased , and therefore the oxygen content is decreased . However the Hb saturation and the PO2 are normal in anemia . ( pO2 is determined by the dissolved O2 and not by the oxygen attached to Hb)
Now, the Hb saturation refers to the following : up to 4 oxygen molecules can be attached to each Hb molecule depending on the pO2 : when pO2 is approx 100 mm Hg : 97% saturated, which means that all four sites are occupied by an oxygen molecule ; at pO2 =40 mm Hg , 75 % saturated ( only sites 1, 2 and 3 have an oxygen b/c the 4th site has the lowest affinity for O2 and therefore requires a higher pO2 to maintain attachment. ) When Oxygen is delivered to the tissues, the carrying capacity is not changed , what changes is the affinity of the Hb for oxygen ( it decreases b/c the pO2 is lower.) Hope this helps !

05-26-2006, 04:07 PM
In cases of CO posioning, does your O2 tension (P02) decrease? I would think no b/c CO does not interfere w/ the dissolved O2 level. However, don't you also get a left shift in C0 toxicication? So won't you get a lower Po2 @ at given O2 content?
I know that O2 content will decrease b/c there is a decrease amount of oxyhemoglobin, is this the right reasoning? Thx a million. very weak at arterial gases and pressures.

05-26-2006, 04:29 PM
Hey, Jack.. You're right..
In CO poisoning, the pO2 is normal and the Hb concentration is normal. The problem is that CO has a lot higher affinity for Hb than O2 so all CO is attached to Hb which means that the oxygen saturation is lower and the oxygen content is lower ( b/c oxygen content is primarily determined by the oxygen attached to Hb ) So there is a shift to the left and the carrying capacity is decreased in CO poisoning. In anemia , the carrying capacity is decreased. hope it helps a little ...

05-26-2006, 07:17 PM
I thank you very much for your help....Are you preparing for your step I also or have you taken it already? Where you from? Thanks once again/

05-26-2006, 08:04 PM
I am done with Step 1 ; I wrote it a couple of months ago.. Good luck with your studies !!

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