Chapter 8 Implications of Abnormal Hydration Status
incidence of renal disease in this population (2). Using a BUN:Cr ratio greater than 20:1 produces high preva- lence rates of dehydration. BUN can be low as a result of low protein intake, celiac disease, liver cirrhosis, hemodialysis, malnutrition, syndrome of inappropriate antidiuretic hormone, or liver disease. Serum creatinine may be low because of muscle wasting (2,24). When unadjusted for other contributing causes, a BUN:Cr ratio should not be used as the sole criterion for diag- nosing dehydration.
Serum osmolarity should be either directly mea- sured or calculated due to its sensitivity (2). This mea- surement can rise in dehydration with as little as a 1% change in body weight. Plasma sodium and osmolarity will be significantly elevated during dehydration caused by insufficient fluid intake.
The Dietary Reference Intake (DRI) for water includes all water contained in food, beverages, and drinking water. Per the DRI, total water requirements vary by whether one is male or female. The electro- lytes in the body include sodium, potassium, chloride, calcium, phosphorus, and magnesium; sodium is the substance of most concern when replacing fluids lost through exercising. Electrolytes are needed for electro- chemical reactions within cells. A lack of electrolytes in the body can interfere with chemical reactions needed for healthy cell operation.
Dehydration may be further defined by the type of fluid/electrolyte imbalance that exists (19). Knowing which type of imbalance is present in moderate to severe cases of dehydration can ensure that appropriate replace- ment fluids restore the proper balance of fluids and elec- trolytes to the body (6).
“Failure to match intake and loss of water and minerals, especially sodium and potassium, may lead to dehydration. Depending on the ratio of water to electrolyte loss, dehydration can be classified as iso- tonic, hypertonic, or hypotonic” (6). Water and sodium have a close interrelationship.
Isotonic Dehydration
In isotonic dehydration, sodium concentration is less than 130 mEq/L (40). It is characterized by “isotonic loss of both water and solutes from the extracellular fluid; that is when both water and sodium are lost in equivalent amounts. There is no osmotic shift of water from the intracellular space to the extracellular space.” This may occur through vomiting and diarrhea or by taking medications such as diuretics that increase urine output (41). This type of dehydration is sometimes referred to as isonatremic dehydration. GI fluid losses through diarrhea, vomiting, or excessive GI ostomy output put older adults at risk for isotonic dehydration.
127
Isotonic dehydration manifests in numerous clini- cal ideologies. Health care professionals need to monitor older adults who have any of these symptoms, which may include nausea, anorexia, weakness, decreased urine output, no longer wanting to drink, and having numerous physical signs such as dry tongue, sunken eyes, and dry skin with poor skin turgor. Monitoring body weight when dehydration is sus- pected is extremely important. Taking daily weights can be time-consuming but should be completed in cases where dehydration is either anticipated or suspected.
Those with isotonic dehydration are diagnosed using the individual’s history, clinical manifestations that are identified by the health care professional, criti- cal thinking, and laboratory values such as increased red blood cells, hemoglobin, and hematocrit; normal levels of sodium and chloride; changes in urine-spe- cific gravity, specifically an increase when dealing with isotonic dehydration; and arterial blood gases that show acidosis.
Isotonic dehydration is treated by determining and then removing the causes. Often the person is provided isotonic saline, which contains 154 mmol/L Na+ 154 mmol/L Cl− 142 mmo1/L Na+ saline, chloride (Cl−
and
. One must remember that serum is and 103 mmo1/L Cl−
. In isotonic ) concentration is 50 mmo1/L
higher than that in serum; consequently, if the older adult is given too much isotonic saline without normal renal function, it can cause hyperchloremic acidosis. Therefore, giving a balanced salt fluid is often better for treating isotonic water deficit (40). After correcting isotonic dehydration, the older adult must be monitored for hypokalemia related to excessive excretion. Fluid replenishment decreases the concentration of exiting potassium. Potassium must be given if urine excretion is more than 40 mL/h (40). A summary of what happens in isotonic dehydra-
tion is in Table 8.1 (see page 128). The course of cor- rection is to provide both fluid and sodium to rehydrate.
Hypotonic Dehydration Hypotonic dehydration, also called water and electrolyte deficit, hyponatremic dehydration, or volume and elec- trolyte depletion, occurs when sodium loss exceeds water loss. In older adults, hypotonic dehydration can occur when diuretics are used along with a low-sodium diet. Other causes include glucocorticoid deficiency, hypothyroidism, and syndrome of inappropriate antidi- uretic hormone secretion (SIADH) (17).
It also happens in some instances of high sweat or GI water losses or when water and electrolyte deficits are treated with water replacement only. It is
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