Basic Concepts of Fluid and Electrolyte Therapy

2. Definitions
Much confusion in the diagnosis and treatment of fluid and electrolyte
disorders is caused by loose and ambiguous terminology. The
term ‘dehydration’, for example, meaning lack of water, is often used
carelessly and imprecisely to include salt and water lack or, even more
confusingly, intravascular fluid depletion. We therefore make a plea
for the use of precise diagnostic terms, which indicate clearly the
deficit or excess and the treatment required.
Anabolism – the synthesis of large molecules from small ones, e.g.
protein from amino acids or glycogen from glucose.
Catabolism – the breakdown of large molecules into small ones, e.g.
protein to amino acids or glycogen to glucose.
Total body water (TBW) – percentage of body composition consisting
of water, approximately 60% of body weight, less in obesity and more
in infants.
Intracellular fluid (ICF) volume – that part of the TBW contained within
the cells, approximately 40% of body weight and 2/3 rds of TBW.
Muscle cells contain 75% water and fat cells have