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Retired NBME 21 Answers

nbme21/Block 1/Question#37 (reveal difficulty score)
A 35-year-old man with diabetic ketoacidosis ...
Serum potassium concentration ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—an_improved_me(91)
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@blackcoffee;

Insulin does play a role in bringing back K+ into cells via modulation of K+/H+ exchange. This is because it helps to address the ketoacidotic state of the patient. By bringing pH closer to baseline, there is return of K+ into the cells, while H+ comes back out of the cells.

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an_improved_me  However, you are right, in that too my knowledge, that is not the main way insulin influences K+; it is more via the NaATPase as you have mentioned. +1



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submitted by โˆ—nala_ula(127)
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In diabetic ketoacidosis, there is increased acid in the extracellular space. According to FA there is a transcellular shift due to decreased insulin that leads to more H+ entering the cell in exchange for K+. This leads to hyperkalemia with depleted intracellular stores of K+. There is also osmotic diuresis that leads to increased K+ loss in the urine and total body K+ depletion. The question asks that is most likely to decrease with insulin therapy: serum potassium concentration will decrease as K+ is now exchanged for H+ inside the cell.

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cienfuegos  Additional UW fun facts regarding Potassium and DKA: use caution giving insulin and IV fluids to dehydrated hyperglycemic because i forces K in cells causing fast decrease of extracellular Potassium, thus give K supplementation even when serum K elevated +3
linwanrun1357  Why urine K+ does not decrease? +3

This explanation is faulty. Insulin causes K to go inside via upregulating NaKATPase activity. Nothing to with H+ exchange as far as Insulin is concerned.

H and K exchange is separate from this.



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submitted by โˆ—peachespeaches(2)
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I agree that Serum K decrease is the better answer, but wouldn't Urine K also decrease once blood sugar goes down with insulin treatment (i.e. osmotic diuresis would lessen)?

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