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NBME 22 Answers

nbme22/Block 2/Question#40 (22.4 difficulty score)
A previously healthy 7-year-old girl is ...
Serum potassium concentration🔍

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AF 0192, pg 785

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 +  
passplease  Why do you not get an increased bicarbonate concentration? +  
briangibbs3  Bicarb acts as a buffer and binds up excess H+ in DKA +  

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

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 +  

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

drdoom  super high blood glucose; super high glucose spillage into urine; lots of peeing = volume depleted (“osmotic diuresis”) +  
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. +  
alphatnf  *where the vast majority of your K is inside your body +