Fundamentals of Anaesthesia - Body Fluids

Question 1

How much of total bodyweight does total body water comprise in a young adult male? And in a young adult female? Why can there be large variations between individuals?

Answer 1

Water comprises 60% of the body weight of a young adult male.

TBW in the adult can range from 45% to 75% of body
weight. This large variation is the result of individual
differences in adipose tissue, which contains relatively
little water.

In the young adult female TBW only forms about 50% of body weight. This difference between the sexes develops during puberty and decreases in old age due to a reduction in adipose tissue.

Question 2

How much of TBW forms ICF? And ECF?

And plasma (% of total body weight)?

Answer 2

ICF = 60% (27L in a 70kg adult including 2L RBC contents)
ECF = 20-45% (decreases with age, around 7.5L per sq metre of body weight)
Plasma = 5% total body weight