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Old 04-14-2010
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Default metabolism imbalance

An 18-year-old woman has gastroenteritis with nausea and vomiting and is able to ingest only small amounts of water. After 3 days, she develops light-headedness, especially when sitting or standing. Arterial blood gas analysis is most likely to show which of the following sets of values?

pH - PCO2(mm Hg) - HCO3-(mEq/L)
(A) 7.30 - 28 - 15
(B) 7.30 - 55 - 27
(C) 7.40 - 40 - 24
(D) 7.50 - 30 - 22
(E) 7.50 - 47 - 35
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Old 04-14-2010
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E is the ryt ans in my opinion
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Old 04-14-2010
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Quote:
Originally Posted by doctorF View Post
E is the ryt ans in my opinion
that was fast! and yes u are ryte.
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Old 04-14-2010
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Can you please explain why we should think of alkalosis?
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Old 04-14-2010
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If I am not that wrong again (doctorF should remember ), this is a typical case of hypochloremic hypokalemic metabolic alkalosis, due to persistent loss of fluid through the upper GI tract. Poor water intake only adds to volume contraction, which in turn aggravates this contraction alkalosis.

Activation of the renin-angiotensin-aldosterone axis increases Na+/H+ exchange & decreases HCO3- reabsorption at the PCT of the nephron, as well as increasing H+ excretion at the DCT (through the intercalated cells).
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Old 04-15-2010
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well dr. ath's explanation was exactly correct (its like out of a book!!)

however i cant always remember explanations like this so a quick way i think when i come across these questions:

vomiting causes met alkalosis (because u lose acid from yr stomach)
diarrhea causes met acidosis (because u lose alkali from yr intestine)

now i see the HCO3- (met alkalosis would be >24) and as a compensation, the resp CO2 has increased a bit to compensate.

oh n the pH must follow vomiting (met. alkalosis)
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Old 04-15-2010
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After repeating high-yield concepts over & over again, I suppose I have learned a few things by heart (although I HATE parroting ). And of course you are right about the rest; vomiting=met. alkalosis vs. diarrhea=met. acidosis (this is the way I actually remember them, too!). But, as you have understood till now, I dare not to post a comment if I don't have a concise mechanism in hand .
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