Intravenous fluids and blood component therapy

For practical purposes the body may be considered as a solution of solid materials in water contained within a recipient. The solid materials have distributed this water in compartments. Constant exchange of solids and fluids exists among the compartments. In order to understand exchange mechanisms between body water compartments and solids, the body water may be classified by location as intracellular and extracellular. The latter may be further divided into intravascular, interstitial, and intralymphatic. In addition, small amounts of fluid may be encountered in the healthy state in body cavities (intestinal, pleural, pericardial, joint, spinal, intraabdominal), known as third space. These fluids are relatively unresponsive to the physiologic mechanisms governing the other compartments and are unimportant in healthy condition. In disease states, third space cavities may acquire an important role by accumulating large amounts of fluid and may pose significant problems in fluid management.