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[de- + hydration]
1. The removal of water from a chemical, e.g., by surface evaporation or by heating it to release water of crystallization.
SYN: SEE: anhydration
2. The clinical consequences of negative fluid balance, i.e., of fluid intake that fails to match fluid loss. Dehydration is marked by thirst, orthostatic hypotension, tachycardia, elevated plasma sodium levels, hyperosmolality, and, in severe instances, cellular disruption, delirium, falls, hyperthermia, medication toxicity, renal failure, or death.
DEHYDRATION RESULTING FROM SWEATING
Worldwide, the most common cause of dehydration is diarrhea. In industrialized nations, dehydration is also caused by vomiting, fevers, heat-related illnesses, diabetes mellitus, diuretic use, thyrotoxicosis, and hypercalcemia. Patients at risk for dehydration include those with an impaired level of consciousness and/or an inability to ingest oral fluids, patients receiving only high-protein enteral feedings, older adults who do not drink enough water, and patients (esp. infants and children) with watery diarrhea. Older adults (esp. those over 85) are increasingly hospitalized for dehydration. Dehydration is avoidable and preventable. Lengthy fasting before a procedure, long waits in emergency departments, or increased physical dependency, e.g., being unable to pour water from a bedside container, may place patients at risk. Nursing home residents are at higher risk for dehydration than older adults living independently, partly because of limited access to oral fluids. Older adults also are at risk because of reduced thirst-response, a decrease in total body fluids, and declining renal function. Clinical states that can produce hypertonicity and dehydration include a deficiency in synthesis or release of antidiuretic hormone (ADH) from the posterior pituitary gland (diabetes insipidus); a decrease in renal responsiveness to ADH; osmotic diuresis (hyperglycemic states, administration of osmotic diuretics); excessive pulmonary water loss from high fever (esp. in children); and excessive sweating without water replacement.
Dehydration should not be confused with fluid volume deficit. In the latter condition, water and electrolytes are lost in the same proportion as they exist in normal body fluids; thus, the electrolyte to water ratio remains unchanged. In dehydration, water is the primary deficiency, resulting in increased levels of electrolytes or hypertonicity.
The patient is assessed for decreased skin turgor; dry, sticky mucous membranes; rough, dry tongue; weight loss; fever; restlessness; agitation; and weakness. Cardiovascular findings include orthostatic hypotension, decreased cardiovascular pressure, and a rapid, weak pulse. Hard stools result if the patient's problem is not primarily watery diarrhea. Urinary findings include a decrease in urine volume (oliguria), specific gravity higher than 1.030, and an increase in urine osmolality. Blood serum studies reveal increased sodium, protein, hematocrit, and serum osmolality.
Continued loss of water is prevented, and water replacement is provided as prescribed, usually beginning with a 5% dextrose in water solution intravenously if the patient cannot ingest oral fluids. Once adequate renal function is present, electrolytes can be added to the infusion based upon periodic evaluation of serum electrolyte levels. Health care professionals can prevent dehydration by quickly treating causes such as vomiting and diarrhea, measuring fluid intake (and where possible urine output) in at-risk patients, providing glasses and cups that are light and easily handled, teaching certified nursing assistants (CNAs) and family care providers to record fluid intake, observing urine concentration in incontinent patients, offering fluids in small amounts every time they interact with an at-risk patient, encouraging increased amounts of fluids (at the patient’s preferred temperature) with and between meals and at bedtime (to 50 oz or 1500 mL/day unless otherwise restricted), and offering preferred fluids and a variety of fluids (including frozen juice bars, water-rich fruits and vegetables), and assessing for excessive fluid loss during hot weather and replacing it.