Читать книгу Laboratory Assessment of Nutritional Status: Bridging Theory & Practice - MARY LITCHFORD - Страница 11

Disorders of fluid balance include dehydration and overhydration. Both present challenging physiological conditions that can be addressed using NCP. Inappropriate interventions can create additional problems.

Dehydration is the most common fluid electrolyte disorder of frail older adults living in community or institutional settings (Lavizzo-Mourey, 1988). Since no single measure has proved to be the ‘gold standard’ in the diagnosis of dehydration, it is often overlooked or misdiagnosed (Faes, 2007). Dehydration is a special concern for the hospitalized patient and long-term care resident. It is one of the most frequent diagnoses for admission to the hospital for patients 65 years and older. Mortality of patients with dehydration is high if not treated adequately and in some studies exceeds 50 percent (Bourdel-Marchesson, 2004). In terms of morbidity, several studies have shown an association between severe dehydration and poor mental function (Seymour, 1980; Wilson, 2003). Other studies found that dehydration was a significant risk factor for developing thromboembolic complications, infectious disease, kidney stones and obstipation (fecal impaction) (Embon, 1990; Wrenn, 1989).

Total body water accounts for about 60 percent of total body weight of middle-aged adults and about 45 – 50 percent of total body weight of elderly adults (Narins, 1994). The clinical significance of these numbers is that the elderly reach clinical dehydration faster than younger adults. Total body fluids decline in the elderly primarily because of a change in body composition. With age, older adults tend to lose lean muscle mass and gain fat. Lean muscle mass contains a higher percentage of water than fat which contains very little water. Changes in fluid balance in seniors can have a dramatic impact on their health and well-being (Chidester, 1997; Inouye, 1999; Rauscher, 2001; Welch, 1998).

Persons who are seriously ill and older adults tend to have a decreased thirst sensation due to confusion, an altered state of consciousness, or severe depression. Dehydration can occur during episodes of illness, fever, diaphoresis and inadequate replacement fluids. Fluid needs increase by 7 percent per degree of fever measured in Fahrenheit and by 12 percent per degree of fever measured in Celsius.

Early signs of dehydration include:

•Headaches

•Fatigue

•Loss of appetite

•Flushed skin

•Poor skin turgor

•Heat intolerance

•Lightheadedness

•Dry mouth and eyes

•Dark urine with strong odor(Kleiner, 1999)

Maintenance of fluid balance is essential to good health and recovery from surgery, illness or injury. Increased fluid losses are associated with:

•Chronic or acute infections

•Fever

•GI losses

•Vomiting

•Diarrhea

•Laxative abuse

•Gastric drainage

•Ileostomy

•Excessive urinary losses

•Diuretics

•Glycosuria

•Diabetes insipidus

•High-protein diet

•Environment

•Elevated ambient temperature

•Low humidity

The decrease in body fluids causes reductions in both the extracellular and intracellular fluid compartments. Clinical manifestations of dehydration are closely related to intravascular volume depletion. Without treatment, dehydration progresses to hypovolemic shock, organ failure and death (Ellsbury, 2003).

Assessment FOR Dehydration

Assessment for dehydration in the hospitalized patient or long-term care resident involves:

•Physical assessment

•Recent history of food and fluid intake

•Laboratory assessment

During a dehydrated state, there is less water in the body. The concentration of blood constituents increases. The laboratory tests may present a misleading picture of the individual’s nutritional status. There are three types of dehydration based on serum sodium:

•Hypertonic dehydration

•Isotonic dehydration

•Hypotonic dehydration

Hypertonic dehydration occurs when body water losses are greater than sodium losses. This can be due to reduced oral intake, excessive losses from sweating or prolonged high fever. The sodium concentration rises in the extracellular compartment, which draws water osmotically from the intracellular fluids. A summary of laboratory tests used to diagnose different types of dehydration follows on Table 4. Additional information about each laboratory test is in the next section of this text.

Isotonic dehydration occurs when the body loses equal amounts of sodium and water. Gastrointestinal disturbances causing extreme diarrhea and/or vomiting can trigger isotonic dehydration. This type of dehydration is often seen with food borne illness or severe bleeding. The serum sodium levels, serum osmolality and specific gravity levels are within normal ranges. These individuals are not thirsty and do not sense the need for more fluid. Both fluid and sodium are needed to rehydrate the patient. Refer to Table 4.

Hypotonic dehydration occurs when the body sodium loss exceeds water loss. This is sodium depletion or hyponatremia. It occurs in the patient who is taking diuretics, on sodium restricted diets, experiencing diarrhea or vomiting, has excessive sweating, a renal sodium-wasting syndrome or a combination of these contributors. There is typically a reduction in extracellular fluid volume. The laboratory tests indicate abnormally low serum sodium levels. Treatment includes giving water-electrolyte solutions to rehydrate the patient. Refer to Table 4.

Table 4. Screening for Dehydration

Lab Test	Hypertonic	Isotonic	Hypotonic
Osmolality (S)	>Normal	WNL	< Normal
Sodium, (S)	> Normal	WNL	< Normal
Hemoglobin	> Normal	> Normal	> Normal
Hematocrit	> Normal	> Normal	> Normal
Albumin, (S)	> Normal	> Normal	> Normal
BUN	> Normal	> Normal	> Normal
Urine Specific Gravity	> Normal	> Normal	< Normal

Key: WNL= within normal limits

Assessment FOR Overhydration

Overhydration occurs when there is an increase in the extracellular fluid volume. The fluid shifts from the extracellular compartment to the interstitial fluid compartment. This is called edema and is typically caused by one of these mechanisms:

•capillary hydrostatic pressure (CHF)

•colloid osmotic pressure (hypoalbuminemia)

•capillary permeability (inflammation)

•Lymphatic obstruction (following surgery)

•Organ failure (kidney or liver)

•physical activity

Overhydration is categorized by serum sodium concentration levels which reflect the composition of the fluids retained. Each type of overhydration presents different pathophysiologic effects. There are three types of overhydration:

•Isotonic overhydration

•Hypertonic overhydration

•Hypotonic overhydration

Overhydration or edema is commonly seen in patients with congestive heart failure, low blood pressure, renal insufficiency, liver failure (ascites) and physical inactivity. The fluid retention is usually a symptom of a bigger medical problem.

Edema is usually treated with loop diuretics. Overdose of loop diuretics can cause extracellular fluid depletion and a potassium deficiency. The success of loop diuretics is measured by a significant weight loss and a decrease in edema. Laboratory tests will change rapidly as edema diminishes. Typical lab values seen in edema are summarized in Table 5. Additional information about each laboratory test is in the next section of this text.

Table 5. Screening for Overhydration

Lab Test	Hypotonic	Isotonic	Hypertonic
Osmolality (S)	< normal	WNL	> normal
Sodium, (S)	< normal	WNL	> normal
Albumin (S)	< normal	WNL or slightly low	< normal
H/H	< normal	WNL or slightly low	< normal
BUN	< normal	WNL or slightly low	< normal

Key: WNL= within normal limits