NBME 20 Answers : Block 1 : #37 = A 1-month-old male newborn is brought to the ...

nbme20/Block 1/Question#37

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

Na⁺: 132; K⁺: 3.2; Cl⁻: 90; HCO3⁻: 37

+2 upvote downvote
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

+2 upvote downvote
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