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NBME 24 Answers

nbme24/Block 4/Question#40

A 25-year-old woman is brought to the emergency ...

Pulmonary capillary leakage

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submitted by neonem(262),

This patient isn't hypoventilating, they're HYPERventilating, hence the PCO2 < 40 mm Hg.

Let's walk it backwards: They are hyperventilating to compensate for the metabolic acidosis caused by widespread hypoxia. Hyperventilating allows you to blow off more CO2.

Why are they hypoxic? The person is hypoxic due to inflammation and acute respiratory distress syndrome from the pneumonia. All the cytokines from the inflammatory cells cause increased pulmonary capillary leakage, which blocks up the alveolar membrane so that O2 can't get through to the blood.

Why do they have metabolic acidosis in the first place? No oxygen --> no electron transport chain and no TCA --> lactic acidosis.

 +1  upvote downvote
submitted by sattanki(31),

The pt is having a severe case of pneumonia/sepsis (ARDS?), as that’s why her PO2 is low at 64. So in pneumonia there is increased capillary leakage leading to pulmonary edema.

 +1  upvote downvote
submitted by famylife(37),

From AAFP:

"Acute respiratory distress syndrome is a manifestation of acute injury to the lung, commonly resulting from sepsis, trauma, and severe pulmonary infections. Clinically, it is characterized by dyspnea, profound hypoxemia, decreased lung compliance, and diffuse bilateral infiltrates on chest radiography...

In ARDS, the injured lung is believed to go through three phases: exudative, proliferative, and fibrotic, but the course of each phase and the overall disease progression is variable. In the exudative phase, damage to the alveolar epithelium and vascular endothelium produces leakage of water, protein, and inflammatory and red blood cells into the interstitium and alveolar lumen. These changes are induced by a complex interplay of proinflammatory and anti-inflammatory mediators."


 +1  upvote downvote
submitted by dbg(26),

Did anyone else wonder WHAT "PULMONARY SYMPTOMS" is the question referring to?? There is literally not a single symptom mentioned in the whole vignette. No "crackles heard over both lung fields" are not symptoms. They are signs found by the physician.

Seriously doubting the whole NBME board test writers right now. Do they adequately revise their work? This is not the first technical mistake I realize on the new forms.

nbmehelp  Yup. Looking back its clear what they were trying to get at, but this definitely threw me off when I was taking the test bc I kept rereading the question looking for a specific symptom the pt had that they wanted me to explain. +1  

How do you know her pulmonary symptoms are due to pulmonary capillary leakage and not hypoventilation? Is pulmonary capillary leakage just another way of saying pulmonary edema?

sattanki  Hypoventilation in no way leads to pulmonary edema. +  
fenestrated  Hypoventilation would increased the PCO2 +