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Old 06-14-2011
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Calculator Calculating the Interstitial Fluid Volume

a 22 year old man participates in a research experiment in which ISFV must be determined.
his 22Na space is 15.2L
125I-albumin space is 2.9L
3H2o space is 41.3L
his hematocrit is 43%
what is ISFV of this man in liters?

a)5.3
b)12.3
c)18.1
d)26.1
e)34.8
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Old 06-14-2011
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ISFV = Interstitial fluid volume

Total body water = 3^H2O = 41.3L
Extracellular fluid = 22^Na = 15.2L
Plasma volume = 125^I-albumin = 2.9L
Hematocrit = 43%

Blood volume = Plasma volume / (1 - Hematocrit)
ISFV = Extracellular fluid volume - Plasma volume = 15.2L - 2.9L

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Old 06-14-2011
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y------> ?
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Old 06-14-2011
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do u have the right answer? i think is B.
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Old 06-14-2011
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As explained by bebix:

I think all you need here is:

Total ECF Sodium, and Total Albumin.

ECF will tell you total sodium distributed in both ISF and Plasma.
Plasma Volume = Albumin only

So Plasma Vol = ECF - Interstitial Volume.

15.2 - 2.9

= 12.1

I dont think this is USMLE style question, I think its just meant to clear your concept of ICF-ECF
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Old 06-15-2011
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ECF volume=plasma vol+ISFV..
ISFV=ECF vol- plasma..
=15.2-2.9
=12.3
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