Organization and composition of body fluids

Disorders of fluid balance and electrolyte homeostasis are commonly observed in critically ill patients and in those who require emergency anaesthesia. Consequently, anaesthetists and intensive care physicians must understand the physiological principles that govern fluid balance. This article discusses the compartmentalization of total body water and describes methods by which the volume of the fluid compartments may be measured. The novel concept of the endothelial glycocalyx is discussed in addition to the conventional and contemporary models of capillary filtration dynamics. The core elements of fluid balance and cardiovascular homeostasis are also explored.