The ability of the body to adjust fluids, electrolytes, and acid-balance is influenced by:
Infants and growing children have much greater fluid turnover than adults because their higher metabolic rate increases fluid loss. Infants lose more fluid through the kidneys because immature kidneys are less able to conserve water than adult kidneys. In addition, infants respirations are more rapid and the body surface area is proportionately greater than that of adults. Increasing insensible fluid losses. The more rapid turnover of fluid plus the losses produced by disease can create critical fluid imbalances in children much more rapidly than in adults.
In elderly people, the normal aging process may affect fluid balance. The thirst response often is blunted. Antidiuretic hormone levels remain normal or may even be elevated, but the nephrons become less able to conserve water in response to ADH. Increased levels of atrial natriuretic factor seen in older adults may also contribute to this impaired ability to conserve water. These normal changes of aging increase the risk of dehydration. When combined with the increased likelihood of heart diseases, impaired renal function, and multiple drug regimens, the older adult’s risk for fluid and electrolyte imbalance is significant. Additionally, it is important to consider that the older adult has thinner, more fragile skin and veins, which can make an intravenous insertion more difficult.
GENDER AND BODY SIZE
Total body water also is affected by gender and body size. Because fat cells contain little or no water and lean tissue has a high water content, people with a higher percentage of body fat have less body fluid. Women have proportionately more body fat and less body water than men. Water accounts for approximately 60% of an adult man’s weight, but only 52% for an adult woman. In an obese individual this may be even less, with water responsible for only 30% to 40% of the person’s weight.
People with an illness and those participating in strenuous activity are at risk for fluid and electrolyte imbalances when the environmental temperature is high. Fluid losses through sweating are increased in hot environments as the body attempts to dissipate heat. These losses are even greater in people who have not been acclimatized to the environment.
Both salt and water are lost through sweating. When only water is replaced, salt depletion is a risk. The person who is salt depleted may experience fatigue, weakness, headache and gastrointestinal symptoms such as anorexia and nausea. The risk of adverse effects is even greater if lost water is not replaced. Body temperature rises, and the person is at risk for heat exhaustion or heatstroke. Heatstroke may occur in older adults or ill people during prolonged periods of heat; it can also affect athletes and laborers when their heat production exceeds the body’s ability to dissipate heat.
Consuming adequate amounts of cool liquids, particularly during strenuous activity, reduces the risk of adverse effects from heat. Balanced electrolyte solutions and carbohydrate-electrolyte solutions such as sports drinks are recommended because they replace both water and electrolyte lost through sweat.
Other factors such as diet, exercise, and stress affect fluid, electrolyte and acid-base balance.
The intake of fluids and electrolytes is affected by diet. People with anorexia nervosa or bulimia are at risk for severe fluid and electrolyte imbalance because of inadequate intake or purging regimens (e.g. induced vomiting, use of diuretics and laxatives). Seriously malnourished people have decreased serum albumin levels, and may develop edema because the osmotic draw of fluid into the vascular compartment is reduced. When calorie intake is not adequate to meet the body’s needs, fat stores are broken down and fatty acids are released, increasing the risk of acidosis.
Regular weight-bearing physical exercise such as walking, running, or bicycling has a beneficial effect on calcium balance. The rate of bone loss that occurs in postmenopausal women and older men is slowed with regular exercise, reducing the risk of osteoporosis.
Stress can increase cellular metabolism, blood glucose concentration and catecholamine levels. In addition, stress can increase production of ADH, which in turn decreases urine production. The overall response of the body to stress is to increase the blood volume.
Other lifestyle factors can also affect fluid, electrolyte, and acid-base balance. Heavy alcohol consumption affects electrolyte balance, increasing the risk of low calcium, magnesium, and phosphate levels. The risk of acidosis associated with breakdown of fat tissue also is greater in the person who drinks large amounts of alcohol.