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Old 07-22-2012
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Lungs Oxygenation Reduced the Aa Gradient!

A patient with hypoxia breathes 100% O2 for several minutes, and his PAO2/PaO2 gradient decreases from 35 mm Hg to 30 mm Hg. Which abnormality best explains the cause of the original hypoxia?

A) Anatomic shunt blood flow
B) Hypoventilation
C) Pharmacologic depression of brainstem neurons
D) Pulmonary diffusion impairment
E) Ventilation/Perfusion mismatch
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Old 07-22-2012
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A. Anatomical shunt
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Old 07-22-2012
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my choice E.......
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D ......????
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Old 07-22-2012
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A I think
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Old 07-22-2012
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If PAO2/PaO2 gradient is decreasing from 35 to 30mm, what does that mean,
is hypoxia is improving ?

somebody explain plz...

Last edited by curiousmind; 07-22-2012 at 07:39 AM.
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Old 07-22-2012
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Everywhere in FA and Goljan contain only description of increased or normal A-a gradient.
So, i guess is A.
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Old 07-23-2012
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Default correct answer :)

Correct answer is A) Anatomic shunt blood flow

I was also a bit confused btw A and E. I was thinking that maybe in ventilation/perfusion mismatch, I mean in decreased perfusion with ventilation ok, breathing with 100% 02 would cause vasoconstriction and hence a drop in arteriolal P02...

Here's the official explanation:
The fact that breathing pure O2 for several minutes had little effect on the difference between arterial and arteriolar PO2 suggests that as quickly as O2 entered arterial blood, it was “diluted” with oxygen-poor venous blood. This would be most likely to happen in the presence of an arteriovenous shunt.

As for E) - Ventilation/perfusion mismatching does lead to arterial hypoxemia, but it is usually not suspected until the three other potential causes of hypoxemia (i.e., hyperventilation, thickened respiratory membranes, and anatomic shunts) have been ruled out. Oxygenation typically improves the PAO2/PaO2 gradient substantially.
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