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NBME 22 Answers

nbme22/Block 2/Question#27

A 50-year-old man who has smoked 2 packs of ...

Increased blood HCO3−

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submitted by armymed88(19),

emphysema leads to CO2 trapping leading to increase paCO2 in the blood, which gives you a respiratory acidosis Proper renal compensation will increase bicard reabs and decrease excretion- giving you increased bicarb in the blood

meningitis  Increased blood HCO3 could have easily been interpreted as increased blood pH aswell. FOllowing your explanation, since the pt had acidosis, the increased HCO3 will just make it a normal pH. Another way to think of the question is: if there is decreased exhalation due to COPD --> increased CO2 --> increased CO2 transported in blood by entering the RBC's with Carbonic Anhydrase and HCO3 is released into blood stream. So increased CO2 -> increased HCO3 seeing as this type of CO2 transport is 70% of total CO2 content in blood. +8  
drmohandes  I thought you could never fully compensate, so your pH will never normalize. Primary problem = respiratory acidosis → pH low. Compensatory metabolic alkalosis will increase blood HCO3-, but not enough to normalize pH, it will just be 'less' low, but still an acidosis. +  

can anyone please explain why option E which is increased in Urinary pH is not the correct answer. becasue hydrogen wasting is also a form of correcting respiratory acidosis.