Fluid and electrolyte balance

Monitoring and manipulating body fluid and electrolytes form a crucial aspect of nursing care. For the average male, only about 18% of the body weight is protein with 15% fat and 7% minerals; 60% is water. For health, body water and electrolytes must be maintained with a limited range of tolerances. Homeostatic mechanisms regulate parameters such as body fluid volume, acid-base balance (pH) and electrolyte concentrations, maintaining a delicate, dynamic balance which can be destablished during illness. In extreme cases, the fluid or electrolyte deficit can lead to death. Consequently, nurses must have a clear understanding of fluid and electrolyte homeostasis so that they can assess fluid and electrolyte status, anticipate/recognise deterioration and implement corrective interventions. Nursing interventions in relation to fluid therapy may range from encouraging the patient to drink an afternoon cup of tea to managing a complicated intravenous fluid regimen. Ill-defined terms, such as 'restrict fluids' or 'push fluids', and instructions to record fluid intake/output or daily weight, are commonly encountered. However, without a knowledgeable appreciated of the physiology and patho-physiology of fluid and electrolyte balance there is a real risk that these tasks will be performed in a somewhat mechanistic fashion, without sufficient thought or understanding. This chapter reviews the normal mechanisms which regulate body fluid and outlines some of the basic adaptive responses to stress. The regulation of acid-base balance is also considered, along with basic principles in the management of fluid and electrolyte disorders. Throughout the chapter, typical clinical situations where fluid and electrolyte control may be compromised are reviewed. Reference is made to the ethical dilemmas which may be associated with the administration/withdrawal of hydration measures.