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NBME 21 Answers

nbme21/Block 1/Question#5 (44.6 difficulty score)
A 45-year-old woman is brought to the ...
Absorption atelectasis🔍

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submitted by nosancuck(73),
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hBur lte me eltl oyu a lli recste

EPPE nsptrvee attlAeseisc KAA tad GNUL APCLLEOS

tnDo be wiorryn tobua mdraon wrdso ethy ustp ni trofn of eth HIHG DEILY nsoe

hungrybox  literally LOL'd lmao I love this +8  

bronchus obstruction traps oxygen in alveoli no nitrogen able to enter (atmospheric air entering body (78% nitrogen and 21% oxygen, nitrogen is so important nitrogen bc it is a poorly absorbed gas and thus is in charged of keeping alveoli inflated) oxygen in the alveoli is absorbed into the blood reducing the volume of the alveoli alveolar collapse absorption atelectasis

bethune  Why is pulmonary hypertension incorrect? +  
samsam3711  PEEP allows the alveoli to remain slightly open with exhalation to prevent atelectasis. Pulmonary Hypertension is going to be related to vascular changes (instead you might see shunting of blood in areas of poor ventilation) +1  
drzed  Pulmonary HTN occurs because of pulmonary vessel vasoconstriction. This can occur d/t multiple factors, but one of the most important ones is hypoxic vasoconstriction that the lungs will undergo (for example, at altitude). In the setting of PEEP, you are ventilating the lungs perfectly; this allows for the pulmonary vessels to open up and not undergo vasoconstriction. Thus, you prevent pulmonary hypertension via hypoxia. +  
peridot  @drzed by your logic, you're arguing for D to be the answer but the correct answer was about preventing atelectasis +  
medstudent  The question is what’s key. The purpose of PEEP is to keep the airway open. The purpose of ventilation with supplemental oxygen can help with preventing pulm HTN. Could be wrong, but that’s what makes sense to me. +  

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submitted by haliburton(191),
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I osehc ieindcarcog meaed, but I ieevebl hist is nicrertoc cbaseeu heret si on ahert feilrau rksi ta shit e,itm so eth rppuseo fo teh PEEP si ytncilrea not to pshu uot l.dufi

bighead478  doesn't there have to be an airway obstruction (mucus, foreign object etc.) in order for this to happen? 100% O2 without any airway obstruction should not cause absorption atelectasis, right? +  
iloveallpotatoes  And Tension Pneumothorax is wrong bc PEEP would furthur exacerbate that. +1  
hyperfukus  @iloveallpotatoes yea i realized that now after getting it wrong :( +  
plzhelp123  @bighead478, they are using a cuffed endotracheal tube and mechanically ventilating this patient which is creating an iatrogenic "obstruction" and as @haliburton mentioned, having a high FiO2 leads to over-absorption by the blood which leads to absorption atelectasis if no other gas is allowed to enter/there is no communication with atmospheric pressure during expiration. Thus, we add positive end-expiratory pressure which keeps alveoli open at the end of expiration to prevent collapse +