With dehydration, all fluid compartments are affected. Dehydration results from inadequate fluid intake in the presence of increased fluid losses. Assessment of blood electrolyte concentrations and determination of acid-base status are performed using techniques that reflect conditions in the extracellular fluid compartment.ĭehydration is a common feature of many diseases. When fluids are administered to dehydrated sheep or goats, fluid losses are replaced within the extracellular fluid compartment therefore the fluids being administered should contain concentrations of ions similar to those found in the extracellular fluid compartment. Chloride and bicarbonate are the major anions within the extracellular fluid space, whereas phosphates, proteins, and other anions maintain electroneutrality with the potassium cation in the intracellular fluid compartment. The concentrations of sodium and potassium are maintained within and outside of cells by the Na +,K +-ATPase pump. Potassium is the major intracellular cation. Sodium is the most important cation within the extracellular fluid compartment, accounting for about 95% of the total cation pool. The movement of water and electrolytes between compartments is governed by hydrostatic and oncotic forces. Although the intracellular and extracellular fluid compartments differ in electrolyte composition, they are in osmotic equilibrium and water can freely diffuse between them. The reticulorumen is an important reservoir of fluid for adult animals during periods of water restriction, and the gastrointestinal tract also can be a site for water deposition during disease processes such as grain overload or endotoxemia. The interstitial fluid compartment consists of fluid surrounding cells, cerebrospinal fluid, connective tissue, and most importantly, the contents of the reticulorumen and the rest of the gastrointestinal tract. The extracellular fluid compartment can be further subdivided into the intravascular fluid or plasma volume (5% of body weight) and the interstitial fluid (15% of body weight). ![]() Approximately two thirds of total body water is intracellular fluid (40% of body weight), and one third is extracellular fluid (20% of body weight). Total body water is distributed within two major compartments, extracellular fluid and intracellular fluid. Estimations of total body water for fattened sheep are approximately 50% of body weight. ![]() 2 Overweight sheep and goats have decreased total body water content compared with that in lean animals, because adipose tissue contains very little water. The larger total body water and extracellular fluid volume in the neonate do not provide a reservoir of fluid for the sick animal in these species. By the age of 6 months, values for total body water and extracellular fluid volume are similar to those in adults. The larger total body water percentage is due primarily to a large extracellular fluid volume. In general, neonatal lambs or kids have relatively more body water than adults, and total body water in neonates may approach 75% to 80% of body weight. 1 This percentage can vary with age, body composition, and breed. Total body water makes up approximately 60% of a sheep’s or goat’s body weight. In order to administer fluids and electrolytes properly, a general understanding of body fluid composition for the patient’s species, and of how this fluid is lost during disease states, is necessary.
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