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NBME 21 Answers

nbme21/Block 2/Question#35

A 4-month-old female infant is brought to the ...


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submitted by haliburton(74),

This is water intoxication. https://www.ncbi.nlm.nih.gov/pubmed/1877579

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. +  
temmy  are we just going to ignore the diarrhea for 3 days? what is its significance +  
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 +  

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submitted by jjubilee(1),

Per google symptoms of hypochloremia and hyponatremia are very similar; however, hyponatremia includes seizures and spasms. But per my quick google search hypochloremia does not. Hypochloremia also can present with respiratory difficulties, but I didn't see that with hyponatremia.

hello  That answer choice is hypERchrloremia, not hypochloremia. +  

 +1  upvote downvote
submitted by didelphus(14),

Any idea why hyperchloremia isn't an answer? The diarrhea would cause an normal anion gap (hyperchloremic) metabolic acidosis.

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 +2  
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 +  
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. https://rehydrate.org/diarrhoea/tmsdd/2med.htm#CONSEQUENCES%20OF%20WATERY%20DIARRHOEA +  
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"... +  
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. +