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Nutritional Assessment Calculations


Nutritional Assessment Calculations Notes

This Nutritional Assessment tool is provided to assist the user in the calculation of nutritional needs.  As such, it only provides approximations in the calculation of patient total calories, protein and fluid needs.  Metabolic monitoring and professional assessments must also be performed to assure appropriate patient response.

A NOTE ABOUT ENERGY EXPENDITURE CALCULATIONS

Controversy exists in the literature as to the correctness of equations used in the calculation of energy expenditure.  In addition, questions have also been raised, and studies performed, as to whether or not such equations properly account for the various diverse states in which a patient may be found (e.g., age, weight, injury state, multiple trauma, severe burns, lean body mass, etc.).  As a result, dozens of such predictive equations have been developed over the years.  The User should only use this Nutrition Assessment Calculator tool if they are comfortable and in agreement with the calculation equations used by this program in the calculation of energy expenditure and nutrient requirements.  The results of these calculations should only be used as an input, in combination other nutritional assessments tools, to assist you in your final determination of specific nutrient requirements for individual patients.  These equations are defined in the following paragraphs.

Basal Energy Expenditure versus Resting Energy Expenditure

Two methods are currently in use to calculate nutritional formula needs:  Basal Energy Expenditure (BEE) and Resting Energy Expenditure (REE).  However, another area of disagreement in the literature is in the predictive output of energy expenditure equations.  The literature suggests that energy expenditure equations, such as the Harris-Benedict equation, can be used to predict Basal Energy Expenditure (BEE) (Reference: Frank B. Cerra, Pocket Manual of Surgical Nutrition, p. 59, The C.V. Moseby Company [1984]) and Resting Energy Expenditure (REE) (Reference: Wolinsky & Williams, Nutrition in Pharmacy Practice (NiPP), p. 220, American Pharmaceutical Association [2002]).

Part of this disagreement is a result of the definition of Basal Energy Expenditure:

Basal Energy Expenditure is the energy requirement to maintain life, or to lie at rest while breathing and maintaining cellular metabolism.  It is measured at rest, or an estimate made of the energy requirements at rest, but not asleep in a controlled environment.

Resting Energy Expenditure measurements are typically taken under less restricted conditions than Basal Energy Expenditure measurements.

As noted in the Journal of Parenteral and Enteral Nutrition, Vol 16, Issue 6, 566-568, Copyright © 1992 by American Society for Parenteral and Enteral Nutrition, a significant amount of variation was found in published versions of the Harris-Benedict equation.  Of 24 published versions that were reviewed, eight were found to be sufficiently variant such that errors of 7% to 55% in calculations of nutrition requirements would be produced.  As concluded by this study: “The primary reason appears to be the lack of availability in medical libraries of the original Carnegie Foundation publication by Harris and Benedict.”  (Harris J, Benedict F. A biometric study of basal metabolism in man. Washington D.C. Carnegie Institute of Washington. 1919.)  Some would also argue that according to today's test standards, the Harris-Benedict equation does not estimate BEE, but rather REE, because of how the study was conducted.

For clarification purposes, this Nutritional Assessment tool indicates on its screens the result of its basic calculation output as Resting Energy Expenditure.

A NOTE ABOUT PATIENT WEIGHT USED IN ASSESSMENT CALCULATIONS

When performing patient assessments, it should be noted that some controversy exists over whether to use actual, usual, or ideal body weight.  Therefore, this Nutritional Assessment tool allows the user to enter a weight by which the assessment calculations are to be performed (Assessment Weight).  This assessment weight can be any of actual, usual, or ideal body weight as preferred by the user.


Nutritional Assessment Calculations

The following equations and algorithms are used in Nutritional Assessment.  The conversion factors are:

  • 1 Inch = 2.54 cm
  • 1 Kg = 2.20462262 lbs
(Reference: United States National Institute of Standards and Technology (NIST) [2005])

Patient Weights

The patient weight that is utilized with this tool during the assessment process is referred to as the Assessment Weight.  Assessment Weight is the weight which is associated with the current assessment and is used to calculate the patient’s nutritional needs.  Assessment Weight should be entered by the user.  Several types of Patient Weights can serve as this Assessment Weight:
  • Actual Body Weight.  This typically is the Patient Weight as previously entered by the user facility for this patient in the Patient Record.
     
    Note: When a new assessment is created, it is the Patient Weight, as entered by the user facility for this patient in the Patient Record, which is used as the default value for the Assessment Weight.

  • Ideal Body Weight (IBW) (Kg) is based on the patient’s sex and height. It is calculated as follows:
     
    Males: = 50.0 + (2.3 * height in inches over 60 inches)

    Females: = 45.5 + (2.3 * height in inches over 60 inches)

    (Reference: Wolinsky & Williams, Nutrition in Pharmacy Practice (NiPP), p. 220, American Pharmaceutical Association [2002])

    Note: Presently IBW is only calculated for patient's whose height is 60 inches or taller.  For patient's whose weight is less than 60 inches, the IBW, and associated calculations, are shown as "---".

  • Adjusted Body Weight (Kg) is calculated based on the patient’s Assessment Weight and Ideal Body Weight. It is provided as reference as a patient’s Actual Body Weight may be biased by fluid retention, edema, or ascites. It is calculated as described below.

Percent Ideal Body Weight

Percent Ideal Body Weight = (Assessment Body Weight / Ideal Body Weight) * 100

(Reference: NiPP, page 220)

Adjusted Body Weight & Condition Status

If Assessment Body Weight is less than or equal to Ideal Body Weight, then
 

Adjusted Body Weight = Actual Body Weight

Status is “Normal

If Assessment Body Weight is less than 0.9 * Ideal Body Weight, then
 

Adjusted Body Weight = Actual Body Weight

Status = “Malnourished

If Assessment Body Weight is greater than 1.2 * Ideal Body Weight, then
 

Adjusted Body Weight = Ideal Body Weight + ((Assessment Body Weight – Ideal Body Weight) * 0.4)

Status = “Overweight

(Reference: NiPP, p. 219, 235)

Nitrogen Estimates

Gram of Nitrogen = Grams of Protein
6.25

(Reference: NiPP, page 225)


Resting Energy Expenditure (REE) (Kcal/day)

ASPEN Classification

Age (years)

Kcals/Kg

Males

Females

  Neonate

0.0 - 0.5

108

108

 

0.5 - 1

98

98

  Pediatric

1 - 3

102

102

 

4 - 6

90

90

 

7 - 10

70

70

 

11 - 14

55

47

 

15 - 18

45

40

  Adult &Geriatric

(n/a)

Use Harris-Benedict

Use Harris-Benedict

(Reference: NiPP, page 163)

Harris-Benedict -

Males:
REE = 66 + 13.75 * (Assessment Weight in Kg)
+ 5 * (Height in cm) – 6.8 * (Age in years)
Females:
REE = 655 + 9.5 * (Assessment Weight in Kg)
+ 1.9 * (Height in cm) – 4.7 * (Age in years)

(Reference: NiPP, page 240)

Estimated Energy Expenditure (Kcal/day)

Estimated Energy Expenditure = Mid-point of Recommended Calorie Range

For the Recommend Ranges:

A "Warning" Status condition exists for a nutritional component if the order amount for that component is outside the recommended range.  Otherwise the Status is reported as "Ok".

Recommended Range for Calories (Kcals/day)

Severe Injury: REE * (1.5 to 1.75)
Moderate Injury: REE * (1.3 to 1.5)
Low Injury: REE * (1.2 to 1.3)

Recommended Range for Protein (gm/day)

AW = Assessment Weight
PTF = Patient Type Factor

First determine PTF according to the following table:

Patient Age Classification

Age (years)

Patient Type Factor

Males

Females

  Neonate

0.0 - 0.5

2.2

2.2

 

0.5 - 1

1.6

1.6

  Pediatric

1 - 3

1.2

1.2

 

4 - 6

1.1

1.1

 

7 - 10

1.0

1.0

 

11 - 14

1.0

1.0

 

15 - 18

0.9

0.8

  Adult &Geriatric

(n/a)

1.0

1.0

(Reference: NiPP, page 236)

Second, calculate the high and low limits applying the two factors:

Renal Dysfunction/non-dialysis:(0.5 to 1.0) * AW * PTF * 1 gram/kg/day
Renal Dysfunction/dialysis: (0.8 to 1.3) * AW * PTF * 1 gram/kg/day
Renal Severe Stress: (2.0 to 2.5) * AW * PTF * 1 gram/kg/day
Renal Moderate Stress: (1.5 to 2.0) * AW * PTF * 1 gram/kg/day
Renal Mild Stress: (1.2 to 1.5) * AW * PTF * 1 gram/kg/day

Recommended Range for Fluids (mL/day)

First, determine the Base Fluid Volume according to the following formulas:

For Neonatal Patients less than 1 Kg (AW):
Fluid = 100 to 150 mL/Kg (AW)

  For Neonatal Patients 1 – 10 Kg (AW):
Base Fluid = 100 mL/Kg (AW)

  For Neonatal Patients 10 – 20 Kg (AW):
Base Fluid = 1000 mL + 50 mL/Kg over 10 Kg (AW)

  For Neonatal Patients over 20 Kg (AW):
Base Fluid = 1500 mL + 20 mL/Kg over 20 Kg (AW)

  For Pediatric Patients:
Base Fluid = 1500 mL + 25 mL/Kg over 20 Kg (AW)

  For Adult Patients up to 50 years age:
Base Fluid = 1500 mL + 20 mL/Kg over 20 Kg (AW)

  For Adult Patients over age 50:
Base Fluid = 1500 mL + 15 mL/Kg over 20 Kg (AW)

(Reference: Neonatal – NiPP, pg 190; Pediatric & Adult – NiPP, pg 244)

Second, calculate the high and low limits applying the two factors:
 
Renal Dysfunction/non-dialysis:(0.5 to 1.0) * Base Fluid
Renal Dysfunction/dialysis: (0.8 to 1.3) * Base Fluid
Severe Stress: (2.0 to 2.5) * Base Fluid
Moderate Stress: (1.5 to 2.0) * Base Fluid
Mild Stress: (1.2 to 1.5) * Base Fluid

Infusion Rates

Per-Day rates assume that there will be one container per day:

(unable to display)

(unable to display)

Per-Minute rates are for the entire infusion period.  For taper infusion this includes the start, run, and end periods:

(unable to display)

(unable to display)


See also: Nutritional Assessment Algorithm, Basic TPN Order Entry Calculations

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