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#1
08-13-2011
 USMLE Forums Guru Steps History: Not yet Posts: 324 Threads: 70 Thanked 239 Times in 144 Posts Reputation: 249
Hemodynamics

What amount of fluid should we infuse to get a plasma volume of 1L?
 The above post was thanked by: Hope2Pass (08-13-2011)

#2
08-13-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610
Confused

Ok I will try to work this out so bare with me lol :sorry:

60-40-20 rule

60% is Total Body Water (TBW) out of 100% Body Weight.
40% is Intracellular Fluid Volume.
20% is Extracellular Fluid Volume.

Out of the 20% Extracellular Fluid -
- 3/4th (75%) is Interstitial
- 1/4th (25%) is Plasma

Therefore, to get a plasma volume of 1 L you would need to infuse -

1/4th Plasma of 20% ECF = 1/4*20 = 5% Plasma volume
(hope you're with me so far)

Therefore, in a normal human being weighing 70 kg, the volumes would be as follows -

TBW = 70*0.6 = 42 L
ICF = 70*0.4 = 28 L
ECF = 70*0.2 = 14 L
Interstitial Volume = 3/4*14 = 10.5 L
Plasma Volume = 1/4* 14 OR 0.05*70 = 3.5L

Total plasma volume would be 5% of 70 kg = 3.5 Kg.

... I am confused, I tried to work it out but I'm stuck lol. I dont know how to go further about it

Would you give 20 L of fluid to get 1 L of plasma volume?

5% of 20L = 1L
 The above post was thanked by: struggle (08-13-2011)
#3
08-13-2011
 USMLE Forums Guru Steps History: Not yet Posts: 324 Threads: 70 Thanked 239 Times in 144 Posts Reputation: 249

@hope2pass..good try dude..but the answer says 3L..
I dont know how we can get 3L??
I thought it as 4L..
because I thought that 1part goes to plasma and 3parts goes to ISF
so If we infuse 4L ,1L goes to Plasma and 3L goes constitute ISF.
NOT sure though..

Hope someone will help us with this..:sorry:
 The above post was thanked by: Hope2Pass (08-13-2011)

#4
08-13-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,684 Threads: 213 Thanked 1,600 Times in 660 Posts Reputation: 1610

hm yeah i lost myself half way thru lol

but hey, if we infuse fluid it will be infused into ECF right
then 1/4 will go to plasma

so 1/4 of infused fluid should equal 1L plasma volume

1/4*X=1L
X= 1L * 4
X= 4L

Hm, I think you're right! This way you get 4L ... lol i hope thats the way to calculate it! Im not sure how 3L of infused fluid would give u 1L of plasma volume.
 The above post was thanked by: struggle (08-13-2011)

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