17. Fluids

Question 1

How much is total body water and how do we calculate it?

Answer 1

60%

0.6 x kg

Question 2

Give the standard breakdown of total body water for a 70kg man?

Answer 2

TBW = 60%, therefore 42L

2/3 are intracellular = 28L

1/3 extracellular = 14L

Of extracellular:
3/4 = interstitial, 10.5L
Just under 1/4 = plasma, 3L
Transcellular = 0.5L

Question 3

What is distribution in terms of body water?

Answer 3

The transfer of fluid from one compartment to another, crossing semi permeable membranes e.g. endothelium and cell walls.

Question 4

When we talk about giving IV fluids, what are the three compartments we think about?

How much do they hold?

What is the barriers between them

Answer 4

Plasma = 1/4 of ECF (1/3rd of total)

= Crosses capillary membrane =
Interstitial = 3/4 of ECF (1/3 TBW)

= crosses cell membrane =
ICF = 2/3 of TBW.

Question 5

If we give 1000ml of dextrose, how is it eventually distributed and why?

Answer 5

Dextrose will be rapidly metabolised, leaving water, which will spread across all three compartments.

Therefore:
Plasma = 250
ECF = 83
ICF = 667

Question 6

If we give 1000ml of 0.9% saline, how will it be distributed?

Answer 6

Plasma = 250
ECF = 750

Question 7

If we give 1000ml of colloids, how will they initially distribute?

Answer 7

Plasma = 1000ml