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NBME 23 Answers

nbme23/Block 3/Question#45

A 44-year-old woman comes to the physician because ...

Decreased arterial Pco2

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submitted by seagull(722),

This is a panic attack. Hyperventilation drops pCO2 leading to a respiratory alkalosis. po2 is relatively unaffected (don't ask me how?)

sympathetikey  Yeah haha I had the same conundrum. +  
sajaqua1  If she's breathing deep as she breathes fast, then oxygen is still reaching the alveoli , so arterial pO2 would not be effected. +7  
imnotarobotbut  lmao i'm so freaking dumb i thought she was having alcohol withdrawals because it was relieved by alcohol +  
soph  Maybe Po2 is unaffected bc its perfusion (blood) limited not difusion limited (under normal circumstances). +1  
charcot_bouchard  PErioral tingling- due to transient hypocalcemia induced by resp alkalosis. +1  
rainlad  I believe CO2 diffuses ~20x faster than O2, so increases in her respiratory rate have more effect on her PCO2 than her PO2 +1