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NBME p2ck_form7 Answers

step2ck_form7/Block 2/Question#17 (8.0 difficulty score)
Two hours after emergency repair of a ...
Decreased potassium๐Ÿ”,๐Ÿ“บ

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submitted by thomasalterman(154),

my reasoning:

  • diuretics cause hypokalemia โ†’
  • hypokalemia causes โ†‘ digoxin binding to Na/K ATPase โ†’ cardiac dysfunction (i.e. PVCs)
seagull  They don't specify the exact diuretic. More cause hyperkalemia than not. Also, digoxin causes hyperkalemia (mild). This questions answer is infact opposite to what is a logical conclusion. +4  
drbubs  Most diuretics would lead to hypokalemia. Inhibiting the loop of henle or DCT (loop diuretics and thiazides) causes increased Na to reach to the collecting tubules where aldosterone-dependent transporters reabsorb Na at the expense of potassium leading to hypokalemia. It is why we call diuretics that act on the collecting tubules "potassium-sparing" diuretics. +  

submitted by russnels(12),

Anybody have any good insights as to what is going on here? Does surgery somehow cause hypokalemia? Or does this have to do with digoxin toxicity? I'm not sure how surgery fits in. Thanks in advance!

misscorona  Looking at UpToDate, hypokalemia is listed as one of few postoperative electrolyte abnormalities. Surgical stress releases aldosterone which leads to hypokalemia. Hypokalemia is a known cause of premature ventricular contractions. Digoxin toxicity can cause premature ventricular contractions but it seems like this patient was on these medications prior to surgery and this may be less likely contributor. Side note, digoxin can lead to hyperkalemia. +3  
yotsubato  Ah so it is a BS question.... Ugh. +3  
krewfoo99  I think surgery/stress will lead to increase in cortisol which acts like aldosterone to cause hypokalemia leading to premature ventricular contractions +1  
wutuwantbruv  What @krewfoo99 said is correct, cortisol can "act" like aldosterone because they both bind the same MR receptor which normally inactivates cortisol but in a situation where there is excess cortisol (i.e. Cushings, post surgery/trauma) it can overwhelm the receptor leading to activation --> hypokalemia. +  

submitted by step_prep5(74),
  • Key idea:ย Digoxin toxicity can lead toย premature PVCs (along with other arrhythmias), with digoxin toxicity being more prevalent in setting ofย hypokalemia (less potassium to compete with digoxin for binding to the Na/K ATPase)

submitted by keyseph(44),

My two cents: Abdominal surgery for perforated gastric ulcer probably resulted in hypovolemia, leading to increased RAAS activity and contraction alkalosis. This leads to hypokalemia, which is a factor that predisposes to digoxin toxicity. PVCs are one of the most common digoxin-associated arrhythmias and are often the first sign of toxicity, completing the clinical picture described in this question.