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NBME 20 Answers

nbme20/Block 2/Question#24

A patient with a 1-week history of diarrhea has ...

Decreased arterial Pco2

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submitted by hayayah(536),

Patient has chronic diarrhea leading to metabolic acidosis. Respiratory compensation will lead to decreased CO2 (respiratory alkalosis via hyperventilation).

usmleuser007  Aldo would increase b/c protons are anti-transported with potassium --> leads to hyperkalemia --> aldo activation ADH will also increase b/e of volume loss +1  

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submitted by loopers(2),

Another quick way to think of this is through the formula: pH = HCO3/CO2. Since pH is low and HCO3 is low, CO2 must also be low.