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A 70 kgs man with fixed sodium chloride intake ( 2 mmol/day) is given mineralocorticoid injection for 4 days.He has free acess to water and consumes his usual calorie intake.Excretion of Nacl is as follows:
Day Nacl (mmol)
1 30
2 90
3 180
4 200

If 1 lt of isotonic saline contains 150 mmol of Nacl and weighs 1 kg ,how much will he weigh ( in kgs) at the end of the 4th day ?

Ans : is 72 kgs

Can anybody help me in solving it......


Hi Asmi smiling face

I really didn't get your answer, but I posted your q? in some other forum and some nice guy answered this:


docjp - - 02/23/04 13:55

You have got the question wrong, I have seen this question somewhere, but not able to remember where.... Instead of the 2 mmol of daily intake that you have posted, it should have actually been 200mmol per day.

Normally, to maintain a hemodynamic and electrolyte stability you would excrete the same amount of NaCl that you took in. x.e. Basically 200 mmol of Nacl since you don't want any of it to get retained in the body. If it is retained in the body like this, you will add a salt load daily to the body.

Since the mineralocorticoid injection was given, the patient is now retaining salt, so..........

The 1st day he would retaine 170 mmol of salt. 200-30=170mmol.
Like wise for the 2nd day he retains 110
The 3rd 20mmol and
The fourth 0.

Adding up all the values you see there is a total retention of 300 mmol which is just equal to 150x2 mmol.
150mmol is equal to 1 kg as per the data supplied.
So the patient would have put on 2 kg. of weight by 4 days. His weight now is 72 kg.

Does that answer your question? You might wonder that he is on the Mineralocorticoid for 4 continous days, then why did the output of salt go back to normal on the 4th day, the answer is: ANP Atrial Natriuretic Factor would have kicked in by then.


THANKS KRIS...i appreciate you help smiling face

It was Q from sample USMLE CD..and i too didn't understand it :oops:

Thanks a lot :idea:


Yes the answer is 72 kgs:
If your intake is 200 mmol ( too, too high)
then in 4 days you have an intake of 800 mmol and excretion of 500
At last 800-500= 300 mOsm NaCl ( or better 150 mM NaCl) if 150 mOsm = 1kg, the weight has to be 72 at the end of the fourth day

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