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NBME 22 Answers

nbme22/Block 1/Question#45 (57.9 difficulty score)
A 16-year-old girl is brought to the ...

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submitted by cathartic_medstu(28),
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^^^a lufaetuib lbtae thta wsohs afftces no ctleretoyel ellesv ni alxveasti sv tuscediir sv ingtim.ov

dccArniog ot teh et,bla its hadr ot tell idcturei vs xavealti bsuae yb rsume ylrtlteocsee .oanle eTh irnue otcretleesyl uwlod daelyrmk differ in atth ctiieudr lwil veha iasdnecre CNa/lK/ nda vtlaasxie dlwuo ooflwl the tispeopo trden ereeds)(cd.a r,oeHevw ihwt the aftc hatt UNB si iciesnrgan nda ttha we nca llte serth'e a aolicbtem akllsosai tihw aisyrperrot asisiocd mtonanpecso,i we anc bet on iiestcrud veor

ERXTA NOIF mfor teh ltbea in hte nikl :ebavo

oigmti:nV K[ ec]d lC[ ]dce 3[HCO i]cn H[p ]cni
:Lvatai exs K[ d]ce C[l icn or dec] 3[HOC ced ro icn] pH[ cde ro cin]
:icsrt euiD [K edc] lC[ ]dce OCH3[ cin] Hp[ ci]n

nI neriu rfo g,tinmvoi N/K/aCl will lal be n cdIsedreea rnuie ofr viaexlat ea,sbu /aKN will eb e.adeedcrs Cl is romlan or eIcrasned. de niure rof rdiiteuc s:euab /KNlC/a lilw lla eb idreaecns

rn(deAw gYan rfo sreitePdn)

drdoom  table -> +2  
nootnootpenguinn  The last sentence is nice touch!!! +2  

submitted by drmohandes(84),
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Our ntitpae hsa a cibmtoale slakosila htiw ptr)la(ia yrasepntmoco ryeorrtspia csoi.iads


tbaMieolc lsaosklai β†’ +H osls or 3O-CH na:ig

  • nimog:itv sole H+ a(dn sleo )/-+KlC
  • opol deisrctui: elso H+ dna( K+)


Meocailbt i,aiscosd epilsosb aeucss ni iths xtneot:c

  • ieae/hxdaiavtsrral β†’ eols -C3HO a(dn +)K ; -Cl tnyrospmaceo iecernas (lomarn innoa gap)
  • etaeoaczimald β†’ oesl -3CHO dna( +)K ; H+ aols acessdree ubt otn oeunhg to eceomrov the oaiklassl aseucd yb -3HCO lsso
  • icarpooonsetnl
snripper  This makes sense, thanks! +  
dysdiadochokinesia  I was able to break it down to diuretic or alcohol use and chose alcohol use under the assumption that the patient's serum Cl- levels were low (90; N = 95-105) since Cl- is also lost with vomiting. Im assuming that it was wrong for me to make the association between alcohol use and vomiting. +  
avocadotoast  @dysdiadochokinesia I think we can rule out alcohol use by looking at our patient's history and demographic. A 16yo girl who is dieting and constantly studying probably isnt getting turnt because 1) alcohol has empty calories (defeats the point of dieting), 2) why would you try to study when you're drunk, 3) where will this 16yo in social isolation get alcohol +  

submitted by yotsubato(968),
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Why ncta hsit be ?iaalxvest tohB wodlu ueasc itmbcoale asoaiklsl twhi y.maeia.pkhlo. ?

sup  Laxatives would cause an anion gap metabolic acidosis due to loss of bicarbonate in the stool. You would see hypokalemia though as seen in this question. +1  
miriamp3  it took me a lot of time choosing between laxatives and diuretics and at the end I choose diuretics. but I didn't realize that the only thing I had to do was check if were a anion gap or not. +  
snripper  Why would laxatives cause anion gap MA? Isn't it similar to diarrhea? +  
castlblack  The above comments are incorrect. Diarrhea is a cause of normal-anion-gap metabolic acidosis (D in HARDASS from FA). Laxatives are wrong because they would lower HCO3- but in this scenario it is high. The low K+ and Cl- fits either case though. +4  

submitted by usmleuser007(370),
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This roem llkiye ot eb ecuiitrds hrtaer naht tlexvaias bc/

eth lab dsyut woshs a erlan nifosnutcyd (UBN ;map& Cnieneirta rae va)dtleee

oMts yillke eht natepti debasu oolp te;sdiicur oals skown ot eaucs atnocoinrtc aillkda,so gnola itwh anrel bmopresl hcus sa estraintliti iiehtnrsp

endochondral1  would laxatives also have the low potassium? +1  
link981  My question exactly. And what if they were taking Potassium sparing diuretics? Then laxatives would be more likely or am I mistaken? +  
link981  Also creatine is normal, it's at the higher limit of normal so we can't say there is renal dysfunction. The BUN is elevated because patient has metabolic alkalosis with respiratory acidosis. +  
sweetmed  very important to Remember this: Diarrhea causes metabolic acidosis[from bicarb loss in stool], vomiting & loop diuretics cause metabolic alkalosis. +11  
hello  @usmleuser007 not sure your approach is the best way to think about it. The serum Cr is at the upper limit of normal (1.2). And, even if you calculate the ratio of BUN/Cr, it's 21, which would be a PRE-renal issue. +  

submitted by ninja3232(7),

1) Diuretics cause metabolic alkalosis (contraction alkalosis due to hypovolemia)

2) Diarrhea in general will cause a metabolic acidosis (with NORMAL anion gap) due to loss of K+ and bicarb in the stool (stool has alkaline pH normally).

3) Therefore, laxative abuse normally causes metabolic acidosis BUT chronic abuse can result in metabolic alkalosis due to various mechanisms (response to hypovolemia + more activity of H-K ATP-ase exchanger in the collecting duct due to hypokalemia - you pee out the acid to keep more K+).

submitted by alexb(45),
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Is teh tarp ithw ascnott"n yu"igtnds tjus deupossp ot tsppuro hatt esh ahs a hcpsy ordrsdei dlaeert ot iemtrpsnefoc,i which si why 'essh noigg to eeexmstr ot noltroc rhe ?eiwtgh

rrasha2  No, the constant studying is to trick you into thinking shes abusing amphetamines.Amphetamines decrease appetite so a lot of people abuse them for weight loss. That combined with increased concentration to study all day errrday.. #onehellofadrug +  
rrasha2  forgot to mention, another side effect of amphetamines would be increased BP due to the increased catecholamines..don't forget to keep an eye out for that +1  
dentist  would amphetamines influence electrolytes at all? +  

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.Dec CNla - lgnaere uevmlo Dscolse. K+ - Diruecti (sotm sicretidu, tcpxee K+ rapngsi oesn, ucaes pc+)Iy.Kohn CO3mH-ap;& Hp - mlVuoe osls g-;t& ARSA ;-> osrtealdneo uascse +K a&;pm +H wgsanit &;-gt iolmecatb kisaloa;ls ehS yma be mignotvi as we,ll hciwh is thoenra pbisselo ueasc of .met ca lI.nk a2PCO - pyarriertso mnceaiposnot fro tm.e

hello  Patient has normal Na. +  
hello  Lab data indicates serum bicab not ABG bicarb. +  
hello  oops! just realized bicarb is never given as an ABG haha +