Electrolytes and acid–base: common fluid and electrolyte disorders

Abstract

Disturbances of fluid and electrolyte balance are common in clinical practice, especially in hospital settings, and can be iatrogenic or compounded by inappropriate medical or surgical treatment. Recognition and appropriate management are not necessarily difficult or complex. Although specific formulae and standard protocols can help at the bedside, there is no substitute for an understanding and application of some basic principles of renal and endocrine physiology, which this article sets out. Some knowledge of basic renal physiology (including the transport function along the nephron and its regulation) also makes it easier to understand most clinical disorders of fluid and electrolyte balance. Unfortunately, individuals seldom present with a single acid–base or fluid and electrolyte disturbance, so the challenge is to determine which disorder came first, before rushing in and treating in isolation what might seem initially to be the predominant clinical abnormality. Here, we start by describing the main homeostatic functions of the kidney and, more specifically, the essential workings of its functional unit, the nephron (glomerulus and renal tubule).