Abstract

Water and electrolytes are essential components of the “milieu interieur” of the body, creating an environment which surrounds nearly all cells and through which the metabolites and gases pass to and fro. They are also major intracellular components, being 75% of muscle cells but less than 5% of fat cells. The electrolyte gradient across cell membranes is a prerequisite for cell excitability, signal conduction, transport processes and cell movement. Electrolytes also serve as second messengers, co-enzymes or have structural functions. It is important to consider fluid and electrolyte balance in terms not only of external gain or loss, but also in relation to the shifts, which occur between the internal fluid compartments as a consequence of disease.

Learning objectives

• To understand basic concepts in water and electrolyte metabolism.
• To be aware of the influence of trauma and sepsis on fluid and electrolyte physiology.
• To understand the consequences and treatment of extrarenal losses of water.