pulmonary NBME 2,4,32 - forever07

[ArchivalUser]

32. Two days after a cholecystectomy, a 42-year-old
woman has
shortness of breath. Her temperature is 37.5 C (99.5
F), blood pressure is
110/70 mm Hg, pulse is 103/min, and respirations are
24/min. There is
abdominal tenderness. Examination shows no other
abnormalities. An
x-ray film of the chest shows minimal linear markings
in the right lower
lobe. Arterial blood gas analysis on 45% oxygen
shows:

pH 7.41
PCO2 40 mm Hg
PO2 52 mm Hg

Which of the following is the most likely explanation
for her hypoxia?

A
) Acute respiratory distress syndrome

B
) Atelectasis

C
) Congestive heart failure

D
) Fat embolism syndrome

E
) Pneumonia

F
) Pneumothorax

[ArchivalUser]

heist - 07/25/10 23:28

The hypoxia is very severe. PO2/FiO2 ratio is her baseline CO2 used to be high? And when she's tachypneic, she should have respiratory alkalosis with a high pH. All of these are messed up in the question.

With any etiology of hypoxia whatever it is (pneumonia, atelectasis, ARDS, pneumothorax,...), the patient would be tachypneic to get more O2 as he's hypoxic ==> blow more CO2 ==> resp alkalosis. So it's not just seen in ARDS


For this lady, I believe the question is full of mistakes. This is a surgical question, and I guess surgical people may not be good with acid base disorders. I believe the point made from this question is that she had a surgery on her abdomen ==> pain ==> not good aeration (lest it causes more pain) ==> atelectasis which is seen on the RLL in this lady, right above where her surgery occurred. You don't always see fever with atelectasis.

So answer is B.

[ArchivalUser]

heist - 07/26/10 04:02

Some parts of my post are missing, so I'm posting again with changes:


The hypoxia is very severe. PO2/FiO2 ratio is blow more CO2 ==> resp alkalosis. So it's not just seen in ARDS


For this lady, I believe the question is full of mistakes. This is a surgical question, and I guess surgical people may not be good with acid base disorders. I believe the point made from this question is that she had a surgery on her abdomen ==> pain ==> not good aeration (lest it causes more pain) ==> atelectasis which is seen on the RLL in this lady, right above where her surgery occurred. You don't always see fever with atelectasis.

So answer is B.


=========================

@forever07
I'm not sure I understand you perfectly, but resp alkalosis is due to tachypnea which is seen in hypoxia. So depending on the severity of the underlying etiology (PNA, atelectasis,...), and the severity of the hypoxia, the resp alkalosis would be. Makes sense?

[ArchivalUser]

heist - 07/26/10 04:19

The hypoxia is very severe. PO2/FiO2 ratio is less than 200. So this supports ARDS. But she doesn't have the clinical background (no sepsis, no SIRS like pancreatitis,...). Besides, the CXR didn't show B/L infiltrate. So it's unlikely to be ARDS.
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* Re:2, 4,32
#2155618
heist - 07/26/10 04:19

There's something weird about the question. Her resp rate is 24, meaning she should be blowing CO2 off. Yet, PCO2 is 40 only? This means her baseline CO2 used to be higher? And when she's tachypneic, she should have respiratory alkalosis with a high pH. Yet, she has a normal pH. All of these are messed up in the question.