NBME 20

nbme20/Block 1/Question#37

A 1-month-old male newborn is brought to the ...

Na+: 132; K+: 3.2; Cl−: 90; HCO3−: 37

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submitted by hayayah(216),

With chronic vomiting, you lose electrolytes and a lot of acid. It triggers metabolic alkalosis which is why all the serum values are low (or on the lower end of the normal range) except for bicarbonate.

ergogenic22  decreased K+ (from increased RAAS due to volume loss) and decreased Cl- (loss of HCl from the stomach), Alkalosis from loss of HCl and thus high bicarb. For this reason high to mid range K is wrong +1  

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submitted by masonkingcobra(25),

In metabolic alkalosis, potassium moves into the cells

The loss in volume through emesis triggers RAAS resulting in increased Aldosterone release and further potassium excretion

http://www.labpedia.net/test/116


 +0  upvote downvote
submitted by ark110(0),

But what is the difference between option A and option C (132; 4.9; 90; 35)

sympathetikey  K+ shouldn't increase. It's moving into cells due to metabolic alkalosis. +  
home_run_ball  In the parietal cell of the stomach Hydrogen ions are formed from the dissociation of carbonic acid. Water is a very minor source of hydrogen ions in comparison to carbonic acid. Carbonic acid is formed from carbon dioxide and water by carbonic anhydrase. The bicarbonate ion (HCO3−) is exchanged for a chloride ion (Cl−) on the basal side of the cell and the bicarbonate diffuses into the venous blood, leading to an alkaline tide phenomenon. +  
ergogenic22  RAAS increases from volume loss, and thus more aldosterone leads to low K+ +  
sinforslide  Three reasons for hypokalemia. First, some K+ is lost in gastric fluids. Second, H+ shifts out of cells and K+ shifts into cells in metabolic alkalosis. Third, ECF volume contraction has caused increased secretion of aldosterone. +2