NBME 21 Hyponatremia (NBME Answers)

You must be logged in to vote!

Retired NBME 21 Answers

nbme21/Block 2/Question#35 (reveal difficulty score)
A 4-month-old female infant is brought to the ...
Hyponatremia 🔍 / 📺 / 🌳 / 📖
tags:

+7 upvote downvote
submitted by ∗champagnesupernova3(93)

get full access to all content ⋅ pick a username

Diarrhea causes loss of water, Na and Bicarb. Remember that diarrhea is a cause of non anion gap metabolic acidosis because the loss of bicarbonate is compensated by increasing Chloride reabsorption. So she can have hyperchloremia or hyponatremia due to intake of only free water for 24 hours. But she has SEIZURES so hyponatremia is most likely

get full access to all content ⋅ pick a username

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

You must be logged in to vote!

+5 upvote downvote
submitted by ∗haliburton(224)

get full access to all content ⋅ pick a username

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

get full access to all content ⋅ pick a username

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 +1

You must be logged in to vote!

+3 upvote downvote
submitted by ∗readit(18)

get full access to all content ⋅ pick a username

The key to this question is that the patient is 4 months old and getting water.

Newborns should NOT be getting plain water until after 6 months of age because it can cause hyponatremia --> seizures

get full access to all content ⋅ pick a username

You must be logged in to vote!

+3 upvote downvote
submitted by ∗haozhier(23)

get full access to all content ⋅ pick a username

Why is it not hypoglycemia?? Hypoglycemia can also lead to seizure

get full access to all content ⋅ pick a username

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. +1

fbehzadi 24 hours* +

You must be logged in to vote!

+1 upvote downvote
submitted by ∗drzed(333)

get full access to all content ⋅ pick a username

Perhaps I under-thought this questions, but it is highly unlikely to have HYPER- of anything when consuming large amounts of water, because whatever ion is present is going to get diluted. So in the case of normal gap acidosis from diarrhea, yes there may be an initial hyperchloremia, but the water is going to dilute it out.

Between hypoglycemia and hyponatremia, it is more likely to be hyponatremia because the child had seizures

get full access to all content ⋅ pick a username

You must be logged in to vote!

+1 upvote downvote
submitted by ∗didelphus(70)

get full access to all content ⋅ pick a username

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

get full access to all content ⋅ pick a username

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. 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"... +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. +

You must be logged in to vote!

+0 upvote downvote
submitted by ∗champagnesupernova3(93)

get full access to all content ⋅ pick a username

You must be logged in to vote!

+0 upvote downvote
submitted by ∗umpalumpa(6)

get full access to all content ⋅ pick a username

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.

get full access to all content ⋅ pick a username

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". +

You must be logged in to vote!

Must-See Comments from nbme21

nosancuck on Absorption atelectasis
assoplasty on Free T4
seagull on GM2
lnsetick on Apocrine
niboonsh on NMDA receptors are blocked by Mg2+ at the ...
drdoom on Deletion of a hydrophobic amino acid ...
hayayah on HCO3− transported in the plasma
mcl on Aortic
notadoctor on Usual interstitial pneumonitis
madojo on Genital herpes
hungrybox on Obstruction of the bile duct
jambo2222 on Lung
hungrybox on Mismatch repair
hungrybox on Hydrochlorothiazide