Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

The water contained in the body is divided amongst compartments of differing sizes and compositions. The dynamic balance across these compartments is an essential component of normal physiology. Here, the calculation of these volumes by measuring the dilution of markers able to permeate specific compartments is considered. Furthermore, the potential disadvantages to the approach are discussed. The differences in ionic concentration between intracellular and extracellular fluid are quantified and the effects of greater relative protein concentration within cells are also considered. To illustrate daily fluid balance in a healthy individual, a typical intake and output over 24 hours is quantified before consideration of iatrogenic contributions to this equilibrium. The way in which clinically administered fluids of varying compositions affect the fluid compartments is subsequently discussed. The endogenous processes contributing to volume homeostasis are then deliberated including the detection of fluid imbalance through intracellular and extracellular systems as well as the hypothalamic and renal effector mechanisms. Finally, the regulation of sodium is discussed with examination of the mechanisms controlling natriuresis and the reciprocity with potassium balance. © 2012 Published by Elsevier Ltd.

Original publication




Journal article


Anaesthesia and Intensive Care Medicine

Publication Date





603 - 608