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NBME 21 Answers

nbme21/Block 2/Question#35 (reveal difficulty score)
A 4-month-old female infant is brought to the ...

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submitted by champagnesupernova3(82),
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aiDraher cssuae osls fo ,aewtr Na and bcair.B reemRemb ttah eraharid si a aucse fo nno nniao agp ltbmaeico ociisads sbuaece het sslo fo brtcienaoba si tesocnapdme by nagrnecisi lrohCedi pabtoir.neros oS hes cna evha pyhereacormhil or amteoaripyhn edu ot keanit of olyn efer wrate orf 24 .hosur Btu ehs hsa ISRUSZEE so teaaponirymh is tmso ilkley

drzed  I think the initial hyperchloremia would be quickly diluted out by the large consumption of water, so those two competing processes would likely neutralize the chlorine level, or even make the child hypochloremic. +1  

submitted by haliburton(216),
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sThi is earwt tnit.oiaocnix toh1lvw7hwinw.u9/t7.dp./nb/mpcg8n/ms:b.ie75

thisisfine   Agreed! It's along the lines of those marathon runners who collapse questions. Nothing but water for 24 hours = getting rid of too much sodium. +2  
temmy  are we just going to ignore the diarrhea for 3 days? what is its significance +4  
kard  Temmy, We aint Ignoring the Diarrhea, Actually the most likely electrolytes to get lost with it is sodium> chloride> potassium> bicarbonate... Plus the Water intoxication -> HYPONATREMIA +1  
bronchophony  why not hypoglycemia? +1  
saulgoodman  Because glucose is not an electrolyte, it does not conduct electricity in solution. The question is asking "Which of the following electrolyte abnormalities". +4  
skonys  @bronchophony assuming she doesn't have a glycogen/gluconeogensis prob, she wouldn't be hypoglycemic after 24hrs. FA91 +  

submitted by haozhier(20),
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Wyh si ti ton oipheyay?mg?lc melaycgpiHoy nac laso deal to uziseer

cuthbertallg0od  Same thoughts here, and I think hypoglycemia occurs earlier in kids/infants than in adults (like 8 hours?) -- maybe just more likely to be hyponatremia since Na+ lost in the diarrhea... +2  
fbehzadi  I think mostly the fact that 24 is not gonna reduce his glucose to the point of causing a seizure. +  
fbehzadi  24 hours* +  

submitted by readit(16),
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The kye to hist oqutnies si taht the tpeinat si 4 notshm odl and ngttegi .aretw

Nswronbe osluhd NOT be etitggn plnai teawr unlit ertfa 6 htonms fo aeg baueces it anc acseu toiyrpaehmna --;g&t rizussee

submitted by drzed(262),
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aPhespr I ohr-dunthtueg iths eqtu,snsoi tbu ti is lhihyg lekulyni ot veha RHYE-P of gnyihtna ehnw cgsmnniou garle mtsnaou of rw,ate eacsbue wethvrea ino is nesptre si oingg ot etg detld.ui oS ni eht aecs of olamnr apg soicdsai omrf hr,aaeidr sey eehtr yam eb na lantiii rmeeplah,hoycri btu the ratwe is ngoig to ultied ti uto.

tewnBee cpmgholieyay nda empinhraytao, it si remo liykle ot be ahmiperyonta seeuacb eth dhlci dah szeuries

submitted by didelphus(65),
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Ayn diea hyw omhaeepcihlryr snti' na asrew?n Teh reihaadr dluwo aucse an onmlar niano agp eil)cpehmro(cyhr cbioltmae .sidcasio

charcot_bouchard  this is the problem bet uw and nbme. in uw it would be for sure a gotcha ques. but in nbme they are usually looking for most obvious. also look what they are asking "most likely". baby would dev low Na before acidosis. Thats my 2 cents +29  
temmy  hyperchloremia will not account for the seizure that brought the patient to the hospital. seizures according to first aid is caused by hypocalcemia and hyponatremia +1  
cry2mucheveryday  Children with diarrhoea who drink large amounts of water or other hypotonic fluids containing very low concentrations of salt and other solutes, or who receive intravenous infusions of 50% glucose in water, may develop hyponatraemia. This occurs because water is absorbed from the gut while the loss of salt (NaCl) continues, causing net losses of sodium in excess of water. The principal features of hyponatraemic dehydration are: there is a deficit of water and sodium, but the deficit of sodium is greater; serum sodium concentration is low (<130 mmol/l); serum osmolality is low (<275 mOsmol/l); the child is lethargic; infrequently, there are seizures. +  
cry2mucheveryday  Also, why is this being given formula...? May be lactase deficiency...which leads to osmotic diarrhea...leads to hyponatremia(goljan) Aren't newborns supposed to be kept on exclusive breast milk till 6 months?? +  
hello  @cry2mucheveryday Don't read too much into it. The fact that the baby is receiving formula isn't relevant to answering the Q. Btw, not everyone breast feeds. Additionally, the Q wouldn't make much sense if it said "they ran out of breastmilk"... +1  
hello  @cry2mucheveryday Being on formula then the parents running out of formula is more of a clue for water intoxication. This is typically the scenario that water intoxication presents. However, I suppose if for some reason the baby was being breastfed and the parents switched to exclusively waterfeeding (and no other foods), then water intoxication would also result. +  

submitted by champagnesupernova3(82),
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hraDiear eassuc osls fo atrew, Na dna B.icarb emRrembe htta rraihead si a suace fo non nanoi pag betcailom asoiisdc csubeea the sosl of coteibrnaab is cdmaenposte by icrgnesani idelrhoC nriso.patrebo oS seh anc veah aimryhholpeecr or mpnhiyaaotre deu to tiekan fo onyl fere artwe orf 24 hs.our uBt ehs ash RSZIEESU so hoapeyntirma si somt illkey

submitted by umpalumpa(1),

This kiddo has most likely secretory diarrhea (there are no clues in the question that this is osmotic diarrhea). Due to secretory diarrhea, the pt has eunatremic hypovolemia with hyperchloremia. However, the parents give the infant only H2O for 24 hh, which means that Na and Cl get diluted. It is more likely that the pt gets hyponatremic than hypochloremic considering that, before giving H2O, chloremia was high and Na was low. The low Naemia causes cerebral edema, which leads to seizures.

Glucose can easily be crossed out because is not an electrolyte and the question asks for electrolyte changes.

umpalumpa  Correction of this sentence: "It is more likely that the pt gets hyponatremic than hypochloremic considering that, before giving H2O, chloremia was high and Na was normal (i have mistakenly written "Na was low" above, but I wanted to write "Na was normal". +