III. Estimating Nutritional Requirements (Adults)
If the patient is severely underweight (less than 80% of IBW)
then use Current Weight for nutrient calculations.
If the patient is obese, use:
- Adjusted Body Weight = IBW + 0.25(Usual Weight-IBW).
Ideal body weight can be used for nutritional
assessment purposes. See Appendix E for IBW tables based on height
for males and females.
Most hospitalized patients will require 30 kcals/kg/d. Refer
to Appendix F for detailed information on estimating
energy requirements. Dietitians can also provide more refined
estimates of nutrient requirements. At Harborview Medical Center,
a metabolic cart is available for estimation of energy
requirements. Overfeeding should be avoided.
Protein needs may vary greatly with the metabolic status of
the patient. The average patient receiving nutritional
intervention requires 0.8 _ 2.0 g protein/kg usual body weight. The
obese patient is unusual. Use of usual body weight can result
in overfeeding. It is recommended to use Adjusted Body
Weight (ABW) for reasonable estimation of nutrient
requirements. The goals of nutrition support are to minimize
protein breakdown, preserve lean body mass, promote
protein synthesis, and optimize immune responses. The factors
listed in Table I can be used to estimate protein requirements.
Table I: Estimating Protein Requirements
| Clinical Status |
Protein Requirements (g/kg/day)* |
| Maintenance |
0.8-1.0 |
| Mild to Moderate Depletion |
1.0-1.5 |
| Post-operative |
1.2-2.0 |
*Note: Table based on usual body weight except in obese patients.
A healthy adult ingests approximately 1 mL free water/kcal
of energy, or 35-50 mL/kg body weight/day.
Hospitalized patients usually require 30-35 mL/kg/day. Fluid needs
may also be approximated as 1500 mL per
m2BSA. However, wide variations in fluid intake are normally well tolerated
without producing hypo- or hypernatremia or fluid overload.
Patients with liver disease, renal failure, cardiac or pulmonary
diseases or closed head injuries may require restricted fluid
intakes while patients with nasogastric output, diarrhea,
hypovolemia secondary to burns or trauma, diuresis, fistulae, and
insensible losses may require additional fluids. Insensible losses are
the result of respiration, fecal loss, evaporation, and fever.
Replace diarrhea output volume per volume with normal
saline, nasogastric or fistulous output with 1/2 normal saline,
and evaporation due to fever (250 mL/day for each
oC above 37oC) with sterile water or D5W.
Volume depleted patients should be rehydrated and
electrolytes repleted before initiating PN, i.e. fluid deficits should not
be corrected with amino acid and dextrose solutions. PN
solutions are extremely hyperosmolar and cannot be converted
to an equivalent iso-osmolar volume or volume of free
water. Additional fluids (e.g. normal saline, sterile water) can be
added directly to PN bags, some enteral feeding bags, or can
be administered as boluses in tube fed patients.
Electrolyte requirements for the average adult patient
without significant cardiovascular, hepatic, or renal disease, or
an underlying electrolyte abnormality, or significant electrolyte
loss (e.g. fistulae) are shown in Table II.
Electrolyte needs are adjusted daily based on lab results and current clinical status
of the patient.
Table II: Typical Adult Baseline Electrolyte
Requirements During Nutritional Repletion
| Electrolyte |
Daily Requirements |
Comments |
| sodium (chloride, acetate, or phosphate) |
60-150 mEq |
basal catabolism: 1-4 mEq/kg mild-moderate catabolism: 2-3 mEq/kg severe catabolism: 3-4 mEq/kg |
| potassium (chloride, acetate, or phosphate) |
70-150 mEq |
basal catabolism: 0.7-0.9 mEq/kg mild-moderate catabolism: 2 mEq/kg severe catabolism: 3-4 mEq/kg |
| chloride (sodium or potassium) |
60-150 mEq |
replaced 1 mEq per 1 mEq Na or K unless other salt form specified |
| magnesium (sulfate) |
8-24 mEq |
monitor serum Mg concentration |
| phosphate (sodium or potassium) |
7-10 mMol per 1000 kcal |
severe catabolism or prolonged absence of nutritional intake: 15-25 mMol per 1000 kcal of glucose |
Nutritional repletion therapy increases electrolyte
requirements. During the first 3 to 5 days of re-feeding, patients typically
pass through three phases of electrolyte utilization. During the
first 24 to 48 hours, total body deficits must be replaced. In
the second phase, which may last for several days,
anabolic processes are induced which result in increased
intracellular uptake of potassium and phosphate. After approximately
one week of providing nutritional therapy, electrolyte
requirements become relatively stable.
A wide range of fat intake is generally well tolerated by
most individuals. Current national guidelines recommend limiting
fat intake to less than 30% of total kcals. A higher percent
fat intake may be desired for patients with poor
appetites/limited food intake to increase caloric density of foods (fat contains
9 kcal/g vs. 4 kcal/g in carbohydrates and protein). A
minimum of 2-4% kcals as linoleic acid is required daily to
prevent essential fatty acid deficiency. See Section VI:
Initiating Parenteral Nutrition (page 25) for guidelines on parenteral
lipid administration.
Twelve vitamins and six trace elements are known to
be essential in human metabolism (Appendix
G). Hospital diets (except liquid diets) and enteral formulas are designed
to provide at least the recommended daily allowance of
each known essential nutrient.
Very little information is known about the
micronutrient requirements of catabolic or hospitalized patients.
Table of Contents | IV. Nutritional Therapy Options