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Old 02-23-2012
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Angry calculation without calculation ???

hey guys! i have some difficulties with this questing. i know how to calculate the clearance but the explanation of this question drives me nuts...mark to view: Because in this patient the urin solute concentration is half the plasma concentration, the amount of plasma concentration must be half the urine volume per day. Alternatively, you can calculate clearance: cl=(6L/d * 150 mosm/L) /300 moms/l = 3 L/d
(where the hell does the 6L/d come from????)


A patient with a history of unexplained polydipsia is admitted for evaluation of possible diabetes insipidus. After several hours of fluid deprivation, the following measurements are made:
plasma osmolarity: 300mosm/L
urin osmolarity: 150mosm/L
urin solute output: 900mosm/d
What is the solute clearance?

a) 1.5 L/d
b) 2.0 L/d
c) 3.0 L/d
d) 6.0 L/d
e) unable to be calculated unless plasma volume is also known
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Old 02-23-2012
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no idea
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Old 02-23-2012
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ok...i got it....showering really helps thinking....y think i can shower during my exam?

here we go:

900mosm/d and 150 moms/L -> 6L/d 'excretion'

calc: cl=(150*6)/300 =3 tadddaaaaa.......
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Old 02-23-2012
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Haha, nevermind. We weren't born to be mathematicians after all were we!
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Old 02-24-2012
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Quote:
Originally Posted by MedPharm View Post
ok...i got it....showering really helps thinking....y think i can shower during my exam?

here we go:

900mosm/d and 150 moms/L -> 6L/d 'excretion'

calc: cl=(150*6)/300 =3 tadddaaaaa.......

did not get it still why 900 * 150 = 600 ?? could you please explain in a little detail ...

thanks
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Old 02-24-2012
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Originally Posted by Hitman View Post
did not get it still why 900 * 150 = 600 ?? could you please explain in a little detail ...

thanks
They've given the urine output as 900 mosm/day (which sounds pretty ridiculous, btw!)
And the "osmolality" of urine is 150/L (i.e 150 milli osmoles in 1 litre.)
So how many "litres" would have 900 milli osmoles?

Do that math!
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