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#1
06-14-2011
 USMLE Forums Guru Steps History: Step 1 Only Posts: 343 Threads: 127 Thanked 525 Times in 192 Posts Reputation: 535
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
 The above post was thanked by: bebix (06-14-2011), Claus_CU (06-14-2011)

#2
06-14-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

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

 The above post was thanked by: Claus_CU (06-28-2011), prepink (06-30-2011)
#3
06-14-2011
 USMLE Forums Guru Steps History: Step 1 Only Posts: 343 Threads: 127 Thanked 525 Times in 192 Posts Reputation: 535

y------> ?

#4
06-14-2011
 USMLE Forums Addict Steps History: 1 + CS Posts: 113 Threads: 8 Thanked 89 Times in 61 Posts Reputation: 99

do u have the right answer? i think is B.
#5
06-14-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,175 Threads: 38 Thanked 854 Times in 478 Posts Reputation: 864

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
 The above post was thanked by: Claus_CU (06-28-2011), prepink (06-30-2011)
#6
06-15-2011
 USMLE Forums Guru Steps History: Not yet Posts: 324 Threads: 70 Thanked 238 Times in 144 Posts Reputation: 248

ECF volume=plasma vol+ISFV..
ISFV=ECF vol- plasma..
=15.2-2.9
=12.3

 Tags Physiology-, Step-1-Questions

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