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NBME 22 Answers

nbme22/Block 1/Question#32 (46.8 difficulty score)
A 17-year-old boy is brought to the emergency ...
Hypokalemia🔍
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 +16  upvote downvote
submitted by moloko270(60),
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sols fo udifl girgesrt asnltoeerdo tcnoudipro, os nitatep liwl hvae yetnpirrahmae nda aikeaophmyl as a eusrlt

makinallkindzofgainz  dat RAAS +2  

I realise now that diarrhoea causes hypernatremia! And the reason we give ORS is to restore the blood pressure by giving Na and Glu not to correct sodium level!

My 6 yr of medical education was a myth

+1/- apurva(44),


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doGo fact to timmoc to yommre: you seol cbrbia in teh lotos eec(hn hyw aredahri ausces nnainnoo pga lotmeabic c)osdi,asi dna ysclelapei lsoe auimptsos thwi alteaixv asebu as( demoetnin ni the tisqeonu s).emt wtml.te/nt-oetlhetu/lr-tawr-a/detacbn-naehaiwn--eadiwttrcodoeapod:spsishay./bciostemric

sbryant6  I'm going to go take a big bicarbonate poop now. +20  
happysingh  i would suggest that you look into it a bit more. Why ? Had an nbme question (which confused the shit out of me) cuz, Bluemic Pt. who was abusing Laxatives (had the up & down arrows) and this is what it gave : Laxative Abuse — Metabolic Alkalosis :   ↓K+     ↑Cl-                   ↑pH    ↓HCO3- so one of the points of distinction IS the increase in Cl- with laxative abuse (vs. vomiting, which was a knee-jerk reaction when i hear bulimia) +1  
lola915  I thought diarrhea causes Non anion gap metabolic acidosis @happysingh +1  
texasdude4  easy way to remember : "Bicarb out the Butt" +  



You mostly lose HCO3- and K+ in stool.

Loss of HCO3- leads to a normal anion gap metabolic acidosis (FA2019 pg. 580 'HARDASS'), in which we also see a compensatory increase in Cl-.




I have read all the comments, but none explain why hyponatremia is wrong. There is definitely Na+ in stool....thats why sugar+salt is rehydration for peds diarrheal sickness. Low Na+ causes low EVV explaining the low BP, high HR, pallor, and dehydration. Is it correct but just not as correct as C?

waterloo  I Dont know what you mean by low EVV. But here's my thought process. This pt lost lots of water, and when someone takes a laxative causing them to have diarrhea that will lead to metabolic acidosis. A buffering mechanism for the decreased bicarb in the blood is for H+ to leave cells and K+ to go into the cells. So he has to have hypokalemia (low K+ in serum). They gave him IV fluids, so his BP should be headed back to normal. I would think his RAAS will chill out. But it takes time to correct the acidosis, you're kidney won't just immediately stop reabs bicarb so you're body will still be buffering against the acidosis (H+ out of cell, K+ in). +  
waterloo  sorry, I wrote increased bicarb, I meant DECREASED bicarb in the blood. And also should have written "you're kidney won't just immediately START reabs new bicarb" My Bad, wasn't trying to add to confusion. +  
drdoom  i think by `EVV` author meant `ECV` (extracellular volume). @waterloo, appreciate the explanation but think something is off: loss of HCO3- via diarrhea should result in acidemia, which would oppose the presumption of ‌``H+ leaving cell, K+ going in´´. +  
waterloo  hey so sorry, I must have been super tired posting this. Can't believe I made so many mistakes. Read over it again, and it sounds like gibberish. Wish there was a way to delete. My bad. +  
waterloo  I think I tried to explain too hard. Looking at this question again, I think really the only this is when you lose that much volume, you lose bicarb and K+. Nothing really to do with acid-base. My b. +  
drdoom  no worries! +  
castlblack  EVV = effective vascular volume. Thank you for trying to help but I still don't understand. I still agree with my above mechanism as correct. Whether or not it's most correct idk. +  



 +0  upvote downvote
submitted by apurva(44),

Chronic diarrhoea == Vit D malabsorption = Hypocalcemia (say in crohns)

ACute diarrhoea = Hypernatremia, Hypokalemia, hyperphosphatemia

Dehydration can also cause hyperuricemia and ppt gout attack, but for young pt i think this will be irrelevant




 -1  upvote downvote
submitted by iviax94(7),
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I asw bnetewe alopkyeimha eud( ot ahir)raed nad arpahierecmce/iryymchaueilp cs(nie wtase is hocpoiynt dna udlwo scaue cimpoeryosth umelvo t)acoinctr.no I ntid’d ahve a regta ayw ot dideec bteneew cuprmrraeie/Cpheyyhai so I uigfdre htey wantde .hyoKp Is ehtre a etebrt aolrntaie rfo yhw teh heypr werssan rea icr?onertc

liverdietrying  I think you over-thought this one a little bit with the hypercalcemia/hyperuricemia. Good fact to commit to memory: you lose bicarb in the stool (hence why diarrhea causes nonanion gap metabolic acidosis), and especially lose potassium with laxative abuse (as mentioned in the question stem). https://www.uptodate.com/contents/acid-base-and-electrolyte-abnormalities-with-diarrhea +1  
w7er  Basically they are asking about electrolyte distrubance that cause collapse mainly due to hypokalemia from laxative abuse because diarreha cause hypokamlemia and also cause incrase in renin angiotensin sytem which will further cause hypokalemia resuling cardiocascular colapse :) +  
hyperfukus  i thought the hyperuricemia thing too but i wasn't smart enough to think they wanted hypokalemia like u :( +1