Chapter 8 Implications of Abnormal Hydration Status


BOX 8.1 Consequences of Dehydration ●


Confusion


● Poor skin turgor (elasticity) ● Dry oral mucosa


● Dry furrowed tongue


● Decreased blood pressure Increased pulse


●


● Concentrated urine ● Constipation ● Scanty output


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from renal losses (diuresis) or extra-renal losses (from the gastrointestinal tract, respiratory system, skin, fever, sepsis, or third-space sequestration). Without proper assessment and timely resuscitation, volume depletion can lead to circulatory collapse and shock. Practitioners often use the term dehydration when


they mean intravascular volume depletion. Dehydration and volume depletion are not the same, although they can coexist in the older adult. Dehydration implies a total-body water deficit, alone or in excess of sodium loss, with a subsequent increase in plasma osmolality that usually comes to clinical attention as hypernatre- mia (17). Symptoms of pure water loss arise from the effects of increased osmolality and reflect the cellular responses to hypertonicity. These symptoms can include confusion, thirst, impaired sensorium, and, in more extreme cases, coma or seizures. In contrast, clin- ical symptoms of volume depletion are a result of the hemodynamic effects of the reduction in intravascular volume and usually do not involve neurological changes (2,6).


The consequences of dehydration are many and are often exacerbated in the older adult (17,18). Continued due diligence by the health care practitioner is mandatory.


Dehydration is often classified as mild, moderate, or severe by the percentage of weight loss that has occurred in a short period of time. Mild dehydration is a fluid loss equivalent to less than 5% of body weight, moderate dehydration is about 10% loss, and severe dehydration is 15% or greater loss (19). Severe dehy- dration requires immediate medical attention, as this severity of fluid loss can lead to death.


COMMON CAUSES OF DEHYDRATION


Mild dehydration is common, usually caused by not drinking enough fluids throughout the day. This can be


from just simply not wanting to drink, an inability to drink, or a dependence on others to meet fluid needs. Studies suggest that older adults may not consume fluids for fear of incontinence or difficulty in toileting related to arthritic pain (2,20). The use of thickened liquids, a result of swallowing difficulties, can also place older adults at risk, as many refuse the texture of these beverages. It must be stressed that the vast major- ity of older adults develop dehydration because of disease processes; dehydration is rarely due to neglect by caregivers (21). However, if staffing is inadequate, those older adults who depend on others to meet their fluid needs may not get enough fluids (10). Older adults are very sensitive to heat-related fluid losses, especially in conditions of elevated ambient temperatures (13,14,22) or low humidity. Other causes of evaporative fluid losses may include use of dry oxygen and air-fluidized beds. Excessive urinary losses or polyuria may be caused by diuretics, glycosuria, dia- betes, and chronic renal failure, all leading to dehydra- tion. A number of medical conditions and therapies interfere with fluid homeostasis, including stroke, dia- betes, and congestive heart failure.


Inflammatory diseases of the skin also impact hydration. Few burns are seen in older adults living in long-term care facilities, but with burns, water moves into the damaged skin—the reason for blisters—and can cause dehydration. Other inflammatory diseases of the skin are also associated with fluid loss, as are chronic and acute fever. Fever associated with infec- tions increases insensible losses through perspiration, respiration, and increased metabolism. Water losses increase by 100 to 150 mL/d for each degree of tem- perature above 98.6°F (37°C) (23). Stated another way, fluid needs increase by about 7% per degree of fever measured in Fahrenheit and by 13% per degree when measured in Celsius (24).


Monitoring those receiving tube feedings and those on fluid restrictions is key to preventing dehydra- tion. Calculations should be monitored as well as actual physical signs to ensure adequate fluid intake. Older adults receiving nutrition support can be under- hydrated due to receiving inadequate volumes of nutri- ent solutions or because of hypertonic formulas that lack adequate solute-free water to compensate for the solid solute load of enteral feedings or the hypertonic- ity of parenteral solutions (25).


DEHYDRATION RISK FACTORS Water and sodium balance are closely interdependent. Total body water (TBW) decreases with age (26). This parallels the decrease in total lean body mass (27). Almost two-thirds of TBW is in the intracellular com- partment (intracellular fluid, or ICF); the other one-third


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