Water and Electrolyte Balance: Educating the Patient
Most of the human body's weight consists of fluid. This mixture of water and electrolytes is subdivided into separate and distinct compartments. Various homeostatic mechanisms precisely define the composition and volume of these fluids. The compartments' different chemical compositions are maintained by cell membrane sodium-potassium pumps. Volume and electrolyte imbalances generally occur when fluid gains do not equal fluid losses. This can result in, for example, fluid depletion or a condition known as disordered water balance. By educating patients on the importance of fluid balance, nurses may promote good health.
Fluid comprises approximately 60 percent of a typical adult's weight. The solution generally consists of water and electrolytes. An electrolyte may be defined as "a substance that develops an electrical charge when dissolved in water" (Metheny, 1992, pp. 3-10). Electrolytes which develop a positive charge are known as cations (e.g., sodium, potassium, calcium, and magnesium). In contrast, anions develop a negative charge when dissolved in water. Anionic electrolytes include chloride and bicarbonate.
The total body water (TBW) content of any individual varies according to such factors as body fat content, sex, and age. Fat cells, for instance, contain little water; whereas, lean tissue has a higher overall water content. People who are obese, therefore, generally have less total body fluid than those of leaner build (Metheny, 1992, pp. 3-10).
In every individual, however, total body water is subdivided into various compartments. The two primary compartments are the intracellular space (ICF) and the extracellular space (ECF). The ICF accounts for about two thirds of TBW, or roughly 50 percent of the total body mass. Most of this mass consists of skeletal muscle. On the other hand, ECF comprises only about a third of TBW, or approximatel...