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NBME 22 Answers

nbme22/Block 2/Question#40 (reveal difficulty score)
A previously healthy 7-year-old girl is ...
Serum potassium concentration ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–

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submitted by kobeandming23(8)

DKA (acidosis) > Potassium shifts out of the cell > hyperkakemia

FA 2019, pg 578

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mumenrider4ever  While you will have a high serum potassium, your total body potassium will be low due to very low intracellular potassium (which is where the majority of the body's potassium is usually). This is why you give potassium to patients with DKA +1
passplease  Why do you not get an increased bicarbonate concentration? +
briangibbs3  Bicarb acts as a buffer and binds up excess H+ in DKA +
jurrutia  In other words, DKA a is a cause of metabolic acidosis. Hallmark of MA is low bicarb. +1
skonys  Also INsulIN shifts K+ INto cells. Insulin is used as a treatment for hyperkalemia. This person has DKA thus low Insulin so shes expected to have hyperkalemia because insulin isn't shiting K+ into cells. Theres also the DKA acidosis too. +

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submitted by โˆ—osgoodschlatter10(41)

DKA is a state of decreased insulin; since we know that insulin causes a shift of K+ into the cells low levels of insulin will prevent this and result in hyperkalemia. In addition, due to hyperglycemia and high ECF osmolality water will shift out of the cells into the ECF and K+ shifts out with the water which will futher increase the hyperkalemia

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dentist  I know Insulin cause shift K+ into cells due to closing of ATP-sensitive K channels (blocking K from leaving)? Does it increase K in the cells by another mechanism? +
makinallkindzofgainz  @dentist - Insulin stimulates the Na+-K+-ATPase pump, this drives K+ into the cell (Source: Amboss) +
castlblack  Another mechansim = acidosis causes hyperkalemia due to H+/K+ antiporters. H+ is high in blood so shifts into cells via this antiporter, which shifts K+ out. --potassium section of acid/base chapter in Costanzo physiology +

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submitted by โˆ—skip_lesions(17)

Why would there be hyperkalemia if total body potassium is decreased in DKA?

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drdoom  super high blood glucose; super high glucose spillage into urine; lots of peeing = volume depleted (โ€œosmotic diuresisโ€) +
alphatnf  because insulin normally stimulates Na/K ATPase, which sequesters K inside cell. lack of insulin means that there will be more K outside of the cell causing hyperkalemia. however, you are still total body K depleted due to osmotic diuresis. so the hyperkalemia is mainly due to a shift of K from the intracellular (where the vast majority of your K is inside your body is) to the extracellular space. +1
alphatnf  *where the vast majority of your K is inside your body +

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submitted by โˆ—llpierso(3)

I understand why K+ is increased. But why isn't chloride also increased? This is a metabolic acidosis, so bicarb will be low and H+ will be high. You need an ion to balance charges --> increased chloride?

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llpierso  Nevermind, thought about this more: DKA causes an anion gap acidosis (hence normal chloride and elevated keto-anions). +2

 +0  upvote downvote
submitted by โˆ—empem28(1)

totally buy the answer of K+ being increased, but can somebody explain why her extreme dehydration (decreased skin turgor, excess urine output) wouldn't lead to an increase in serum [Na+]?

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