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.
(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:
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Daily fluid requirement =
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Weight < 1kg
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Weight (kg) x 125 ml/kg/day
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Weight 1 to 10 kg
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Weight (kg) x 100 ml/kg/day
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Weight > 10kg
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2 L/m2/day m2 = square root[weight(kg) x height(cm)/3600]
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(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.
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.
- 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.
(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 |
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Infant
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2.0 to 3.0 gm/kg/day
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Child
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1.5 to 2.0 gm/kg/day
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Adolescent
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1.0 to 1.5 gm/kg/day
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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.
(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.
(see also
Principles of Pediatric Fluid Therapy
and
Introduction to Vitamins)
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.
| 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:
- Sodium requirement determined.
- Sodium from sodium phosphate subtracted from total sodium requirement.
- Remaining sodium added as sodium acetate.
- Any remaining sodium added as sodium chloride
- Potassium requirement determined.
- Potassium added as potassium acetate until acetate requirement met.
- Remainder of potassium added as potassium chloride.
- Acetate determined by amount of sodium and potassium acetates plus acetate from amino acids, determined by concentration.
- 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.
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.
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.
Required trace elements are
added in pre-mixed, fixed combinations, dependent on age and weight.
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SCHOOL OF MEDICINE
