Body composition changes in the critically ill patient: emphasis on water balance.

The moisture contents of foods, fluids, and parenteral solutions taken in and of all samples excreted, the water of oxidation of fuel mixtures burned, and the evaporative water loss must be determined in order to obtain a quantitative picture of water balance. Because there is a tendency to retain water after trauma, surgery, or an acute illness, changes in the water compartment of the body may lead to changes in body weight that may be considered erroneously as changes in energy or protein stores. Measurement of water balance, in addition to calorie and nitrogen balance is one of the most accurate means of accounting for these changes in body composition. Fluid and electrolyte therapy and nutritional supplementation can be tailored to meet the patient's specific needs by utilizing this information. Application of these principles to the care of hospitalized patients outside of the research setting will be discussed.