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NBME 24 Answers

nbme24/Block 3/Question#16

An 18-year-old woman is brought to the physician ...

Respiratory acidosis

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submitted by keycompany(124),

This patient has a pneumothorax. Hyperventillation is not enough to compensate for the overall decrease in lung surface area.

_yeetmasterflex  Could the pneumothorax also cause less ventilation due to decreased lung surface, retaining more CO2 causing respiratory acidosis? That's how I got to the answer at least. +1  
duat98  I think pneumothorax would increase RR because you're probably hypoxic. Also I'm sure when you have a lung collapse on you you'd be scared and that would trigger your sympathetic so your RR will go up either way. +1  
kateinwonderland  Arterial blood gas studies may show respiratory alkalosis caused by a decrease in CO2 as a result of tachypnea but later hypoxemia, hypercapnia, and acidosis. The patient's SaO2 levels may decrease at first, but typically return to normal within 24 hours. (https://journals.lww.com/nursing/Fulltext/2002/11000/Understanding_pneumothorax.52.aspx) +1  
linwanrun1357  How about choice C, --ARDS? +  
bullshitusmle  there is no bilateral lung opacities as you would see in ARDS +1  

 +0  upvote downvote
submitted by jucapami(0),

x-ray corresponds to a tension pneumothorax = imminent respiratory failure if untreated. Right lung is fully collapsed, increasing intra-thoracic pressure, imparing O2 exchange (due to mass effect toward left lung, and collapsed right one), hence accumulating CO2 (in blood), inducing respiratory acidosis.