WASHINGTON UNIVERSITY IN ST. LOUIS SCHOOL OF MEDICINE PEDIATRICS GI PARENTERAL NUTRITION Requirements
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Gastroenterology & Nutrition | Parenteral Nutrition

Nutritional Requirements

Nutritional requirements are stable from day to day and week to week. Decades of clinical research and experience established boundaries for reasonable and safe intakes of carbohydrate, lipid, and amino acids to satisfy nutritional requirments for a wide range of pediatic patients. The PN solutions suggested and designed by this website fall within those established guidelines.



Fluid Requirements

(see also Principles of Pediatric Fluid Therapy)

In the absence of special needs, a rate of 1500 to 2500 cc/m2/day meets fluid requirements. For infants, 125 to 150 cc/kg/day is useful. Small volumes of nasogastric drainage, stool output, or other losses do not require replacement. If salt and water needs far exceed usual requirements, PN is delivered as a standard solution, and the special needs are fulfilled with an additional infusion. The additional fluids and electrolytes can be administered through the same venous access as PN, if only one is present. This approach provides a steady flow of nutrients and allows for maximum flexibility for the primary clinical team to respond to significant short-term changes in patient needs. Frequent alterations in PN solutions produce delays in nutrient delivery and add to the expense of patient care.

Initial fluid requirements are calculated with these weight-based formulas:

  Daily fluid requirement =
Weight < 1kg Weight (kg) x 125 ml/kg/day
Weight 1 to 10 kg Weight (kg) x 100 ml/kg/day
Weight > 10kg 2 L/m2/day m2 = square root[weight(kg) x height(cm)/3600]



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Energy Requirements

(see also Activity, Energy Expenditure and Energy Requirements of Infants and Children)

PN provides calories for total daily energy expenditure (TDEE). TDEE has several components

  • Basal metabolic rate (BMR) or resting energy expenditure (REE) is energy expended while an individual is awake, breathing spontaneously, and resting. The major determinants of REE are age and lean body mass. REE comprises about 60 to 70% of TDEE.

  • Thermal effect of feeding (TEF) is the energy consumed by metabolism of nutrients. Feeding, whether enteral or parenteral, raises metabolic rate, increasing energy requirements. TEF contributes about 6 to 10% to TDEE.

  • Energy for activity represents from 15 to 25% of TDEE in free-living individuals.

  • Growth or accretion of new tissue consumes calories. Synthesis of each gram of new tissue requires 5 to 10 kcal of energy.

Estimation of Energy Needs

The calculation of TDEE of the PN patient requires consideration of each of these energy compartments. In the past, clinicians often overestimated energy requirements in ill patients due to concern that illness, infection, or surgery would increase energy needs. Direct measurements of energy consumption and more careful consideration of changes in energy compartments has led to lower estimates.

  • REE can be directly measured with indirect calorimetry. A metabolic cart measures oxygen consumption and carbon dioxide production from the monitored patient. With various assumptions, caloric expenditure in the resting state is then calculated. Alternatively, REE can be estimated or calculated from mathematical formulas. Actual measurements of REE determined the constituents of these equations.

    • For a child 0 to 3 years,
      REE is approximately 60 kcal/kg/day
    • For a child ages 3 to 10 years,
      REE (kcal/day) = 22.7 x weight (kg) + 495 for males
      REE (kcal/day) = 22.5 x weight (kg) + 499 for females
    • For a child above age 10 years,
      REE (kcal/day) = 66.5 + (5.0 x height)(cm) + (13.8 x weight)(kg) - (6.8 x age)(years) for males
      REE (kcal/day) = 655 + (1.85 x height)(cm) + (9.6 x weight)(kg) - (4.7 x age) (years) for females

    Conditions that increase REE:

    • Fever (8 to 10% for each 1 degree C)
    • Inflammation
    • Burns
    • Pulmonary disorders with increased work of breathing
    • Congenital heart disease with increased cardiac work load

    For most of these conditions, the increase in REE averages only 10 to 20% above estimates. With burns, alterations in metabolism, heat losses, and inflammation can double actual REE above predicted values.

    Conditions that reduce REE

    • Mechanical ventilation
    • Paralysis
    • Starvation
    • Altered body composition, i.e. relatively low lean body mass for weight

  • TEF contributes to energy needs in enterally fed patients adding about 10% to REE.

  • Energy for activity is sharply reduced in hospitalized patients. Most PN patients are bed-bound and inactive. Patients with frequent seizures or constant chorea represent exceptions.

  • Energy for tissue accretion is unchanged. Rapid catch-up growth can increase energy needs. The relatively rapid growth rate of infants in the first few months of life increases TDEE for each kg of weight.

    Considering the possible increases or decreases in each compartment of TDEE:

    • TDEE averages about 1.2 to 1.4 times REE for an awake inpatient. Greater energy needs are unusual.

    • For children less than age 3, their rapid growth rate increases their energy requirement. This extra energy allows for tissue synthesis and accretion. An additional multiplier of 1.25 accounts for this increased energy demand.

    For example, in an infant:

    REE = 60 kcal/kg/day
    Then, 1.25 x 60 kcal/kg/day = 75 kcal/kg/day to allow for bedrest activity.
    But, to synthesize and accumulate new tissue:
    energy cost of new tissue/gm x number of grams of weight gained/day = energy cost of new tissue accretion 5 to 10 kcal/gm x 10 to 20 gm/day = 50 to 200 kcal/day.
    For a 5 kg infant, adjusted REE = 75 kcal/kg/day. Weight gain requires 100 kcal/day or about 20 kcal/kg/day
    TDEE = adjusted REE + energy for growth = 75 kcal/kg/day + 20 kcal/kg/day = 95 kcal/kg/day
    TDEE / adjusted TDEE then equals approximately 1.25.

Provision of Proper Energy Supply

Just right

Provision of sufficient energy provides calories for basic metabolic processes and essential organ function. Catabolic states are avoided, lean body mass is preserved, immune status is maintained, and energy reserves are not depleted. Weight maintenance or gain is monitored to assure adequacy. Morbidity and mortality are reduced. Various anthropometic measurements (skin fold thickness, mid-arm circumference) can be employed to assess nutritional status. None appears more accurate than careful clinical assessment.

Too much

Administration of excessive calories may produce hepatic steatosis and liver dysfunction. High rates of carbohydrate infusion may increase CO2 production, leading to CO2 retention in patients with severe lung disease and limited minute ventilation or diffusion defects. Excessive weight gain adds to fat mass without an equal increment in lean body mass.

Too little

With insufficient energy intake, protein and amino acids are consumed as an energy source, depleting lean body mass. Muscle protein, including essential musculature like diaphragm, is catabolized, leading to a decrease in muscle mass and strength. Continued undernutrition leads to subtle but potentially lethal organ dysfunction. In rapidly growing and developing infants, insufficient energy could affect brain growth and maturation.


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Protein Requirements

(see also Protein-Energy Interactions)

Protein is supplied as commercial mixtures of crystalline amino acids. Trophamine and Travasol are the two commercial mixtures employed in current PN. The constituent amino acid amounts were refined by clinical experience after initial estimates of requirements of essential and non-essential amino acids. Trophamine infusion reproduces the serum amino acid pattern of the post-prandial breast fed infant. It contains taurine as a presumed essential amino acid in growing infants. Cysteine is added. Trophamine is provided to all PN patients three months of age or younger. Travasol infusion is provided to PN patients over three months of age. Glycine and alanine are the major consituent amino acids. Clinical experience supports the safety and efficacy of this mixture.

  Amino acid requirements
Infant 2.0 to 3.0 gm/kg/day
Child 1.5 to 2.0 gm/kg/day
Adolescent 1.0 to 1.5 gm/kg/day


There appears to be a wide range of safety between age groups. Specialized amino acid mixtures designed for specific disease states are available. Nephramine contains only essential amino acids for renal disease patients. Hepatamine contains increased amounts of branched chain amino acids for patients with severe liver disease and hepatic encephalopathy. Insufficient clinical data exists to support strongly the use of these specialized, expensive mixtures in most patients.


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Fat Requirements

(see also Fats and Oils in Human Nutrition)

To meet essential fatty acid (EFA) requirements and to provide additional calories, Intralipid can be infused with the dextrose/amino acid PN solution. To meet EFA needs, 1 to 2% of calories must be supplied as linoleic acid. For an infant, this represents 1 to 2 kcal/kg/day. 20% Intralipid (IL) contains 2.2 kcal/cc and is 50% linoleic acid. Thus, each cc of 20% Intralipid provides 1.1 kcal of linoleic acid. Thus, EFA needs would be met in an infant with 1 to 2 cc/kg/day of 20% IL. For convenience, the IL can be provided as 10 cc/kg/week of 20% IL in a single 24 hour infusion. Similar calculations can be determined for older children. Many patients receiving PN will also be fed enterally. Their EFA needs may be met by enteral intake, reducing or eliminating the need for IL.

As an energy source, IL can be provided in amounts up to 2.5 gm/kg/day in premature infants and 4.0 gm/kg/day in older children. When provided for energy, IL is infused over 12 to 24 hours with a maximum infusion rate of 0.5 cc/kg/hr or 0.1gm/kg/hr in premature infants.


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Electrolytes, Minerals, Vitamins and Trace Elements

(see also Principles of Pediatric Fluid Therapy and Introduction to Vitamins)

Electrolytes

The electrolyte constituents in PN solutions are calculated on the basis of age, weight, and usual maintenance requirements. Because of changes in body composition and rates of weight gain and growth, electrolyte requirements per kg of body weight change with age. Thus, children age 3 years or less require more sodium, potassium, chloride, and acetate than older children and young adults. Electrolyte requirements per 100 kcal of energy consumed remain rather steady throughout life.

Electrolyte and Mineral Requirements mEq/kg/day by Age in Years

Constituent Age < 3 Age > 3
Sodium 3 2
Potassium 3 2
Chloride 3 2
Acetate 4 3
Calcium 1 0.5
Magnesium 0.5 0.5


The concentrations of electrolytes in PN solutions are first determined by using these assumptions. The calculations follow this protocol:

  1. Sodium requirement determined.
  2. Sodium from sodium phosphate subtracted from total sodium requirement.
  3. Remaining sodium added as sodium acetate.
  4. Any remaining sodium added as sodium chloride
  5. Potassium requirement determined.
  6. Potassium added as potassium acetate until acetate requirement met.
  7. Remainder of potassium added as potassium chloride.
  8. Acetate determined by amount of sodium and potassium acetates plus acetate from amino acids, determined by concentration.
  9. Total chloride determined by sodium and potassium chlorides plus chloride from amino acids, determined by amino acid type and concentration.

Any change in cation concentration initiates a recalculation of anion concentrations and constituents. Similar re-calculations occur for changes in anion concentrations. Shifts of salts between chloride and acetate maintain electrochemical balance.

Minerals

Mineral requirements also change with age. Due to rapid bone growth and mineral accretion, infants require higher amounts of calcium and sometimes phosphorus than toddlers and older children. Calcium is added as 1.0 mEq/kg/day in infants and toddlers and 0.5 mEq/kg/day in older children. Calcium can be increased to a maximum of 40 mEq/L and phosphorus to a maximum of 20 mMol/L. Limited solubility in PN solutions precludes higher concentrations of these minerals. Solubility is automatically calculated by an internal formula. Solubility is higher when amino acid concentration is increased.

Magnesium requirement is estimated at 0.5 mEq/kg/day. Magnesium concentration can be decreased or increased. Maximum magnesium concentration is 20 mEq/L.

Vitamins

Necessary vitamins are added as one of two pre-formulated mixtures: MVI-Pediatric or MVI-Adult. MVI-Pediatric is added to PN for children age 10 years or less. MVI-Adult is added for older children.

Trace Elements

Required trace elements are added in pre-mixed, fixed combinations, dependent on age and weight.


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