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NBME 20 Answers

nbme20/Block 1/Question#37 (66.0 difficulty score)
A 1-month-old male newborn is brought to the ...
Na+: 132; K+: 3.2; Clβˆ’: 90; HCO3βˆ’: 37πŸ”,πŸ“Ί
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 +7 
submitted by apop(7),
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sTeeh nasnixpteoal ntera t.erag It deostn elayrl veah hcmu ot do ithw ASRA ictinatoa.v tI sha mlsaot gniteeyhvr ot od wtih a mehnnonpeo llecda teh ilanakle .iedt nI ccirhno vioi,gnmtt yuo odwul tepecx -Cl ot eb low dna K= to eb low sairi(lm ot lba suertls ni eemoons with alb)m.eilu To scnapoteme rof the owl -,lC hte ahtcsom sha na oeptrnitra iwhhc cexensgha Cl- for -CH3O. Tfrheoeer, lC- liwl be enedrielphs ni het atsmo,ch wlehi OH3-C wlil aeicrnes in eht bood,l niascug an isllosaak. nI oiacltakl t,steas the /H+K+ totpenirra ilwl iegbn to c,tiatvea hntfsigi K+ NITO llsec iya(k)mphloea dna aicnnigres .Hp AASR obalbypr pasly a rleo ni mgnkia eht pikyeaaomlh sewro btu teh aankilel edti si moer mttnirpoa .eher

spaceboy98  Isnt alkaline tide related to an increase in pH after meals? Your logic is on point but I'm not sure whether we can apply that concept here. +1  
kevin  concept can be applied here because we need to replete the Cl- in order to create HCl; the stomach doesn't care if Cl- is low in serum, only that Cl- is low in the parietal cells and so will pump out HCO3- in its expense +  



 +6 
submitted by hayayah(1081),
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iWth rnchioc tigvmoin, uyo sloe reltctyoeels adn a tol fo ca.id It igtsrrge bcaolteim ssialkloa chiwh is hyw lal eht msuer lvsuea rea low ro( no eth oewlr den fo the ranoml )rngea petxec ofr a.ictbernabo

ergogenic22  decreased K+ (from increased RAAS due to volume loss) and decreased Cl- (loss of HCl from the stomach), Alkalosis from loss of HCl and thus high bicarb. For this reason high to mid range K is wrong +4  
sbryant6  Wouldn't increased RAAS lead to increased Na+? The answer shows decreased Na+. +3  
sbryant6  Also, remember Bulimia Nervosa is associated with hypokalemia. +1  
sugaplum  so the range they gave for K is 3-6? so 3.2 is WNL then? or are we just operating on "it is on the lower end of normal in peds" +2  
dbg  sodium levels in pyloric stenosis vary, nothing really classic, can be high as in this case simply due to hydration, can low in other cases if aldosterone managed to reverse that to the other extreme +1  



 +4 
submitted by masonkingcobra(346),
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nI mloitacbe lilsakas,o sitsopmau omsve iotn het cells

heT sosl ni mlevou gthurho meseis srrigtge RSAA guelintsr ni endacirse dlrsotoeAne seaelre nad hrtrfeu siasutpom icretoxen

hwiwewept/t/an.dt/11:6/t.bselpta




 +3 
submitted by iamapotato(3),
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oN noe erhe eoebtdrh to yllatacu ssiucds thasw' gigno i .Thnso is a m-1onth dol enwn.rob

He svtmio erfat fd,gsniee ay-5d hirso.yt

At 1 ohtnm ,odl htiw ngitiomv etarf isgen,efd it is mtso elkyli a ecas fo IOYCLPR ETSONSIS deu to rpohepyrthy of het lriocpy creipthsn ullas(yu rouccs 6 eskwe tral)e.

eDu to him miginvot osmtahc sottcnn,e eh liwl LSEO -lC, K,+ dna a+.N

eH llwi AOSL oels H+. sThi is yhw ouy go tino teh ometciabl losskalai itwh a asrtuntel ciensera ni the CH3O.-

kamilia20  sketchy:: vomiting causes loss of WATER greater than sodiumβ†’ increased serum sodiumβ†’ INCREASED serum osmolality, So NA will decrease too, but no that far +  



 +1 
submitted by ark110(1),
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Btu atwh si eth ecfdierfen enetweb notopi A nda ooitpn C ;213( 49.; ;09 )53

sympathetikey  K+ shouldn't increase. It's moving into cells due to metabolic alkalosis. +  
home_run_ball  In the parietal cell of the stomach Hydrogen ions are formed from the dissociation of carbonic acid. Water is a very minor source of hydrogen ions in comparison to carbonic acid. Carbonic acid is formed from carbon dioxide and water by carbonic anhydrase. The bicarbonate ion (HCO3βˆ’) is exchanged for a chloride ion (Clβˆ’) on the basal side of the cell and the bicarbonate diffuses into the venous blood, leading to an alkaline tide phenomenon. +1  
ergogenic22  RAAS increases from volume loss, and thus more aldosterone leads to low K+ +1  
sinforslide  Three reasons for hypokalemia. First, some K+ is lost in gastric fluids. Second, H+ shifts out of cells and K+ shifts into cells in metabolic alkalosis. Third, ECF volume contraction has caused increased secretion of aldosterone. +3  



 +1 
submitted by rainlad(23),
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ieropmHclhyc,o khmlapceioy ioebatclm ilsaoaskl is teh lssccai yeolcteterl dna isceabda- abliemanc fo lcipoyr sosisnet.

Ptertisnse tgionivm srlestu ni ossl fo .HlC eTh rhlcedoi sosl sutelsr in a lwo oldob lirohdec vllee hhiwc piirasm the dsenyi'k iatybli ot cexteer ret.naiobabc Tshi is het tcofar taht teesprnv cinorreoct of eth saioslkla agdniel to almtoeicb kao.alisls

A aeyconsrd syldseoopiertmrnha slveepod edu to het eeadcsred dbloo u.molve The hhig oltearsndoe sleelv sacesu het kesinyd to nrtaei a+N (ot ccerrot the alvarunicatrs ovumle ondepl)ie,t dan eertcex dreinasce auosmnt fo +K inot hte nueri rn(slgeuit in a owl dolbo level of )tmosp.usai




 +0 
submitted by thefoggymist(10),
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I dt'no tge hit.s uhdl'tSon the nsyedki rttsa trriecognc het abbcir lveesl afer 5 asd?y The leddeya phsae of the crtieoncor ecnsi tehy ktea m..e.ti nad ni eth ouintqes 'trehye knisag "w en.o"W vahe ltamieobc osakislal nseic LHC is t,los os eth obyd lliw tyr ot torccer it rtfsi yb ehpntoiyliavnert adn ratle by csandreei reeconxit of r.icabb Bircab uhdlso eb .w.o.l lus(nes 'Im sinsigm sgtnhmioe edu to ienbg ushdx)atee

thefoggymist  Nevermind, I think I got it. Beta intercalated cells cannot function and excrete bicarb because we don't have chloride. Yea apparently I was exhausted. +  



 -2 
submitted by amirmullick3(61),
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Vyre esya oiqetnsu. lnouiobisN vimo.t 1 tmnho a.ge otMs eklily eacnriso si pcyroli .stsnoies

eTh oiitvmgn casesu slso of HCl so we evha eht c,hhayipormleo dan alnre nocaitomneps for isht H lsso yibs riepgrvsne portnos ta eht enexpes of K so htta sveig loeimpy.kaah As eth idsease is anm,ed the redwraro ni the mgaie fo hte soctahm si omohst eslucm poyyrhpther fo hte iocrpyl siamruculs ,oeuscam fgomher tni vaoldiepseh- amss tefl on .apoaltpni ihTs si a ieclamobt skasillao aubcese witohut l-,C the HtrC3 l/aoCOsblaeal rgcehanex liwl tno ,kowr so ouy niaert C3.HO