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Course Sample:
Introduction The frequency of dehydration in health care institutions, especially in the elderly, has required health care professionals to become more aware of how dehydration occurs. Quality of Care issues in long-term care have put a major focus on hydration. Dehydration can result in fines, loss of Medicare funding, lawsuits and negative publicity for long-term care facilities. This series of modules will assist health care professionals in assessing, detecting and treating dehydration in the elderly. WATER BALANCE PHYSIOLOGY The internal body fluids are composed of proteins, electrolytes and other compounds. The human body must maintain a precise homeostatic balance in all body systems to survive. Only small fluctuations can occur without serious consequences. Water is the most abundant substance in the body. The body is 50 percent to 60 percent water, depending on the individual. Dehydration occurs when there is an inadequate water intake or an abnormal fluid loss. "Humans can survive for several weeks without food, but even under optimal conditions, the body cannot endure water deprivation...." (Shoaf, 1991). Fluid balance is an open system which requires daily replacement of fluids and electrolytes. Adequate fluid volume circulates oxygen and glucose to body cells. Adequate fluids are needed to carry away body wastes. Inadequate fluids cause waste products to build up in the blood. Cells with inadequate fluid are starved for oxygen and nutrients. A 10 percent loss of body fluids is serious, and a 20 percent loss of body fluids means death. WATER DISTRIBUTION IN THE BODY Body fluids are kept in balance by water, electrolytes and protein (primarily the serum albumin). The regulation of the body fluids is kept within normal physiological ranges by fluid shifts and osmosis (Porth, 1994; Shils, 1994). Fluids are found in four compartments in the body and kept separate by cell membranes and capillary walls. The largest is the intracellular compartment (ICF). This is the fluid in body cells. Fluid in this compartment allows the important metabolic reactions necessary. There are about 25 liters (each liter is approximately one quart) of fluid. Two thirds of the body fluids are in the intracellular space (ICF). EXTRACELLULAR FLUID COMPARTMENTS There are three extracellular fluid compartments (ECF): the intravascular compartment (IVC); the interstitial fluid compartment (ISF); and the transcellular fluid compartment (TCF). The ECFs contain 15 liters of fluid in the average male. The IVC contains the blood. This is the compartment measured by laboratory tests. This fluid compartment contains five to six liters of blood. Of this volume, one half is plasma and the other half is composed of the cellular content including red blood cells, white blood cells and, platelets. The functions of blood include: - Transporting nutrients, including oxygen and glucose, to all body cells
- Carrying waste products to the kidney and lungs
- Sending antibodies and white blood cells to combat infection
- Circulating heat in the body (Horne, 1993)
The ISF holds lymph fluids and the fluids that surround the cells. The ISF compartment normally contains eight liters of fluid. The interstitial fluid compartment is where edema or "third spacing" occurs. Excess water enters this space, usually due to disease. In the elderly, the most common causes of disease are congestive heart failure, renal failure, and liver disease. The transcellular fluid (TCF) is the final extracellular fluid compartment. The transcellular fluid is in certain body cavities, including the pericardial, cerebrospinal, pleural, synovial and digestive tract. The TCF compartment contains one liter of fluid. Each day large amounts of fluid move in and out of these spaces. The gastrointestinal tract secretes and absorbs about six to eight liters of fluid each day. The four body fluid compartments are about 60 percent of the body weight of men and about 55 percent of the body weight of women. The difference in the fluid composition is related to the higher body fat in the female body. FACTORS THAT INFLUENCE FLUID MOVEMENT The fluid in the body is separated by semipermeable membranes that allow movement of water and solutes (substances dissolved in the water) in and out of body spaces. Some substances pass freely through the membranes while others have limited ability to pass. For example, protein molecules do not pass readily because of their large size. These unique forces keep the fluid and substances in the appropriate space while allowing free movement of nutrients and wastes between spaces. As examples: - Cell membranes separate the ICF from the ISF
- Capillaries separate IVF from the ISF
- Epithelial membranes separate the ISF and IVF and TCF
TRANSPORT MECHANISMS The body fluids have two types of solutes: - Non-ionized solutes, such as glucose and creatinine.
- Electrolytes (carry an electrical charge) such as potassium and sodium.
DIFFUSION Diffusion is the movement of charged or uncharged particles along a concentration gradient (an area of greater concentration to an area of lesser concentration). The non-ionized particles pass freely through cell membrane. Large particles, as protein, usually have very limited passage. Particles that contain an electrical charge, such as electrolytes, sodium, potassium, and chloride, may be allowed partial or limited passage. The solutes with a positive charge are cations. Solutes that carry a negative charge are anions. The old rule about opposites attract applies with diffusion of electrolytes. The rule is: cations will follow anions and anions will follow cations. The amount of solute diffused is increased by a higher temperature, increased concentration of a particle, and decreased by the size of the particle. See the following table to learn the composition of the various solutes that contain a positive or negative charge. These solutes are listed in the table by fluid compartment. COMPARING PLASMA AND INTRACELLULAR FLUID ELECTROLYTES |
