Principles of Fluid and Nutritional Management
FLUIDS
TOTAL BODY WATER
Water is an important solvent in the body and represents a large percentage of body weight in term infants (75%) and an even larger percentage of weight in preterm infants. In the first year of life, total body water (TBW) decreases to about 60%. The percentage of TBW to body weight remains at 60% for males but decreases to 50% for females with puberty. TBW is composed of two main components: intracellular fluid (ICF) and extracellular fluid (ECF). The fetus and newborn have a larger ECF than ICF volume. This changes when the ICF volume increases and the ICF-to-ECF volume ratio reaches adult levels by 1 year of age (i.e., ECF is 20% to 25% of body weight compared with ICF at 30% to 40% of body weight).
The body seeks to maintain a steady state in the regulation of body water. Body water is provided through the intake of fluids and the oxidation of carbohydrates, fats, and protein. Thirst stimulates the intake of water. The kidneys, lungs, skin, and gastrointestinal tract excrete body water. Antidiuretic hormone (ADH) and renal tubular cell response to ADH are the two major mechanisms that affect renal water loss (Feher, 2012).
CALCULATION OF FLUID REQUIREMENTS
The maintenance of fluid balance and correcting imbalances are important in pediatric patients. The nurse should be familiar with the formulas used to calculate fluid requirements in infants and children to verify that the correct amount is ordered and administered.
Maintenance fluids can be calculated using a formula based on body weight:
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A quick method to calculate approximate hourly rate per kilogram weight for maintenance fluid needs is as follows:
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Two examples illustrate how this formula is used:
A 13-kg child would need 1,000 mL + (50 mL × 3 = 150 mL) = 1,150 mL/day, or 47.9 or 48 mL/hour. Using the quick method for calculation of hourly rate, it is 40 mL + (2 mL × 3 = 6), or 46 mL/hour.
A 36.5-kg child would need 1,500 mL + (20 mL × 16.5 = 330) = 1,830 mL/day, or 76.25 mL/hour. Using the quick method for calculation of hourly rate, it is 60 mL + (1 mL × 16.5), or 76.5 mL/hour.
Water is normally lost through urine, insensible loss (skin and lungs), and stool. Maintenance needs may be decreased or increased based on clinical situations. Examples of situations causing increased needs are fever, burns, tachypnea, tracheostomy, diarrhea, vomiting, nasal gastric suction, polyuria, and third space losses (shifts of fluids from intravascular space to interstitial space). Oliguria, anuria, and hypothyroidism are associated with decreased maintenance needs.
LOSS OF BODY WEIGHT DUE TO DEHYDRATION
Clinical signs of dehydration depend on the severity of fluid loss and type of dehydration. Level of dehydration is typically classified as mild, moderate, or severe. Table 5-1 provides an outline for the clinical evaluation of dehydration. Fluid loss can be calculated based on the child’s weight. Divide the weight when dehydrated by weight when healthy and calculate the percent change; then calculate the amount lost by subtracting from 100%. For example, the child’s weight when
healthy is 4.5 kg and current weight is 4.1 kg; divide 4.1 by 4.5 = 0.91 = 91% of healthy weight; 100 – 91 = 9% weight loss.
healthy is 4.5 kg and current weight is 4.1 kg; divide 4.1 by 4.5 = 0.91 = 91% of healthy weight; 100 – 91 = 9% weight loss.
TABLE 5-1 Clinical Manifestations of Dehydration | |||||||||||||||||||||||||||||||
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Quick restoration of circulatory volume is critical for infants and children who are severely dehydrated (10% to 15% dehydration estimate). In these instances, fluid imbalance must be quickly corrected. Fluid boluses of 20 mL/kg of isotonic solution (e.g., 0.9% normal saline or Ringer’s lactate) over 20 minutes intravenously is used to restore circulatory volume (Kleinman et al., 2010).
The child with severe dehydration may need multiple fluid boluses of normal saline at a faster rate. Such boluses should be given as rapidly as possible and repeated until there are signs of improvement in circulation, such as warm skin, improved capillary refill time, and restored urine output. Reassess the child’s status after each fluid bolus. Watch for signs of renal or cardiac failure while administering fluid boluses.
Children who are dehydrated must have their fluid and electrolyte deficits replaced and maintenance fluid needs met. The classification of dehydration based on serum sodium concentration is important in estimating water deficits. Type of dehydration and serum sodium levels is as follows:
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Most children have isotonic dehydration. The fluid management of severe isotonic dehydration is done in a stepped approach, as outlined below.
Intravascular volume is restored.
Receives 20 mL/kg of normal saline bolus(es) over 20 minutes or less until intravascular volume is restored.
Determine 24-hour water needs.
Calculate maintenance water needs per kg PLUS deficit water.
Determine 24-hour electrolyte needs.
Calculate maintenance sodium and potassium.
Calculate deficit sodium and potassium.
Deliver appropriate fluid based on water and electrolyte needs as above.
Administer 1/2 calculated fluid in the first 8 hours after amount delivered as bolus(es) is subtracted.
Administer the remainder of the fluid (second 1/2) over the next 16 hours.
The appropriate fluid for a child with isotonic dehydration is generally D5 1/2 normal saline with 20 mEq/KCl. Children weighing 10 to 20 kg with only mild dehydration typically only need D5 1/4 normal saline. The management of the child with hyponatremic dehydration is generally the same as for the child with isotonic dehydration.
Hypernatremic dehydration is a dangerous situation and puts the child at risk for neurologic hemorrhages and thrombosis. It requires a slower correction of the fluid deficit, usually over 48 to 72 hours. Rapid correction of hypernatremic dehydration can cause rapid fluid shifts, leading to cerebral edema.Electrolyte replacement is calculated and determines the amount of sodium and potassium that is ordered.
caREminder
Do not add KCl until the child voids or until the serum potassium level is determined. Dehydration can be associated with acute renal failure and hyperkalemia. Carefully monitor electrolytes because children with significant dehydration are at risk for disturbances in sodium and potassium levels as well as acid-base balance.
FACTORS THAT AFFECT MAINTENANCE FLUID REQUIREMENTS
Factors that cause alterations in maintenance fluid requirements include the following:
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PRINCIPLES OF ORAL REHYDRATION
Oral rehydration is an acceptable method to replace fluid loss and deliver maintenance fluids in children with mild-to-moderate dehydration from vomiting and diarrhea (Colletti, Brown, Sharieff, et al., 2010; Piescik-Lech, Sharmin, Guarino, et al., 2013; Spandorfer, Alessandrini, Joffe, et al., 2005). Diarrhea can lead to large losses of water and electrolytes and is associated with isotonic dehydration in most patients. Mildto-moderate diarrheal dehydration can be treated in most children with simple oral solutions of glucoseelectrolytes (e.g., World Health Organization oral rehydration salts; Rehydralyte [Ross Products, Abbott Laboratories]) and adequate supervision. For children who are vomiting, oral rehydration solutions (ORS) should begin after 1 to 2 hours of the child or infant having nothing by mouth. Antiemetics are administered to control nausea and vomiting (Niescierenko & Bachur, 2013). Key considerations in oral rehydration therapy include the following (King, Glass, Bresee, et al., 2003; Colletti et al., 2010):
Administer appropriate solution to provide replacement of needed sugars and electrolytes as ordered by the healthcare provider.
For oral rehydration divide the total volume deficit by 4 and aim to deliver this volume of fluid during each of the 4 hours of the rehydration phase. The following amounts of ORS are generally ordered, depending on amount of fluid deficit.
50 to 100 mL/kg—mild-to-moderate dehydration (approximately 12 to 25 mL/kg/hour).
Plus (for both mild and moderate dehydrate) an additional 10 mL/kg for each diarrheal stool and 2 mL/kg for each episode of vomiting.
Begin rehydration with small amounts of the prescribed rehydration solution.
For children younger than 2 years, give 120 mL; for children older than 2 years, give 120 mL to 240 mL slowly every hour, divided into small amounts every 15 to 20 minutes.
If vomiting occurs, give 5 to 10 mL every few minutes until vomiting stops and then greater amounts as above; repeat unless emesis consistently occurs in amounts that exceed intake. A teaspoon or 5-mL syringe can be used for the initial administration of fluid, especially if the child is vomiting. Administer at least 5 mL of solution each minute (5 mL × 60 = 300 mL). In a 10-kg infant this is equivalent to 30 mL/kg. Children larger than 15 to 20 kg can receive 10 mL/minute.
Breast-fed infants should continue breast-feeding during rehydration and after (Farthing, Salam, Lindberg, et al., 2013).
After rehydration, begin feeding immediately. Give infants their regular full-strength formula. If this is not tolerated, the healthcare prescriber may switch the child to a lactose-free formula. Breast-fed infants should continue breast-feeding during rehydration with shorter duration and more frequent feedings. Reintroduce age-appropriate bland solids as soon as tolerated avoiding foods high in simple sugars and fatty foods.
Maintenance solutions with lower sodium concentrations (e.g., Pedialyte, Infalyte) should not be used as rehydrating solutions. Decrease ORS intake if the child appears to be well hydrated or shows signs of fluid overload.NUTRITION
ENERGY NEEDS
The energy needs of children vary depending on age and other conditions. Nutrients (carbohydrates, proteins, and fats) and minerals and vitamins are needed for growth and tissue repair. The energy content of food is referred to as its kilocalorie (kcal) value. Estimated energy requirements are based on basic body metabolism, growth, and
activity. The average kilocalorie requirements for children up to age 3 years are as follows:
activity. The average kilocalorie requirements for children up to age 3 years are as follows:
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An adequate nutritional intake should result in increased weight, height, and head circumference (in infants). Commonly used and easy to remember general rules of weight gain are that infants generally double their birth weight by 4 to 6 months of life, triple their birth weight, and double their length by 12 months of age. The adolescent growth spurt occurs over 24 to 36 months. Growth peaks in females around 12 years and in males around 14 years decelerating by the end of puberty and ceases soon after due to epiphyseal fusion (Lazar & Phillip, 2012).
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