Nutrition Facts and Formulas

Abstract

Adequate nutrition is paramount to optimize survival from critical illness. Many patients in intensive care units cannot or will not take adequate nutrition orally and, thus, supplementation of nutrients via alternative enteral or parenteral routes may be important. The following facts and formulas represent the information necessary for assessment and administration of nutritional support.

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Adequate nutrition is paramount to optimize survival from critical illness. Many patients in intensive care units cannot or will not take adequate nutrition orally and, thus, supplementation of nutrients via alternative enteral or parenteral routes may be important. The following facts and formulas represent the information necessary for assessment and administration of nutritional support.

1 Nutritional Assessment

Total Daily Energy

The total daily energy (TDE) requirements for a patient can be calculated using the following formula:

$$ \mathbf{TDE}\;\mathbf{for}\;\mathbf{men}\;(\mathbf{kcal}/\mathbf{day})=(66.5+13.8W+5H-6.8A)\times (\mathrm{Activity}\ \mathrm{factor})\times (\mathrm{Injury}\ \mathrm{factor}) $$

$$ \mathbf{TDE}\;\mathbf{for}\;\mathbf{women}\;(\mathbf{kcal}/\mathbf{day})=(655.10+9.6W+1.9H-4.7A)\times (\mathrm{Activity}\ \mathrm{factor})\times (\mathrm{Injury}\ \mathrm{factor}) $$

where

• W = weight (kg)

• H = height (cm)

• A  =  age (years)The activity factor is derived as shown in Table 8.1:

  Table 8.1 Activity factor

Injury Factors

The injury factors can be estimated based on the information in Table 8.2:

Table 8.2 Injury factors

Metabolic Rate

The metabolic rate (MR) can be calculated in patients with a pulmonary artery catheter as:

$$ \mathbf{MR}\;(\mathbf{kcal}/\mathbf{h})=V{{\mathrm{O}}_2}(\mathrm{mL}/ \min )\times 60\ \min /\mathrm{h}\times 1\ \mathrm{L}/1,000\;\mathrm{mL}\times 4.83\;\mathrm{kcal}/\mathrm{L}\times 24\;\mathrm{h}/\mathrm{d} $$

where

$V{{\mathbf{O}}_{\mathbf{2}}}\;(\mathbf{mL}/\mathbf{min})=\mathrm{Cardiac}\ \mathrm{output}\;(\mathrm{L}/ \min )\times [\mathrm{arterial}\ \mathrm{oxygen}\ \mathrm{content}\;(\mathrm{Ca}{{\mathrm{O}}_2},\ \mathrm{mL}/\mathrm{L})-\mathrm{mixed}\ \mathrm{venous}\ \mathrm{oxygen}\ \mathrm{content}\;(\mathrm{Cm}{{\mathrm{O}}_2},\ \mathrm{mL}/\mathrm{L})]$

Prognostic Nutritional Index

The prognostic nutritional index (PNI) allows for nutritional assessment of the critically ill patient and is calculated as:

$$ \mathbf{PNI}\;(\%\mathbf{risk})=158\%-16.6\;(\mathrm{alb})-0.78\;(\mathrm{TSF})-0.2\;(\mathrm{tfn})-5.8\;(\mathrm{DSH}) $$

where

• alb = serum albumin (g/dL)

• TSF = triceps skin fold (mm)

• tfn = serum transferrin (mg/dL)

• DSH = delayed skin hypersensitivity (1 = anergy, 2 = reactive)

Probability of Survival

The probability of survival (POS) based on the nutritional status of a critically ill patient can be calculated as:

$$ \mathbf{POS}=0.91\;(\mathrm{alb}) - 1.0\;(\mathrm{DSH})-1.44\;(\mathrm{SEP})+0.98\;(\mathrm{DIA})-1.09 $$

where

• alb = serum albumin (g/dL)

• DSH = delayed skin hypersensitivity (1 = anergy, 2 = reactive)

• SEP = sepsis (1 = no sepsis, 2 = sepsis)

• DIA = diagnosis of cancer (1 = no cancer, 2 = cancer)

Index of Undernutrition

Another way to calculate the nutritional deficit is by utilizing the index of undernutrition (IOU) (see Table 8.3):

Table 8.3 Index of undernutrition

Daily Protein Requirements

The calculation of daily protein requirements (PR) can be done utilizing the following formula:

$$ \mathbf{PR}\;(\mathbf{g})=(\mathrm{Patient}\ \mathrm{weight}\;\mathrm{in}\;\mathrm{kg}) \times (\mathrm{PR}\ \mathrm{for}\ \mathrm{illness}\ \mathrm{in}\ \mathrm{g}/\mathrm{kg}) $$

Nonprotein Caloric Requirements

In order to determine the nonprotein caloric requirements (NCR):

$$ \mathbf{NCR} = (\mathrm{Total}\ \mathrm{required}\ \mathrm{calories})-(\mathrm{Required}\ \mathrm{protein}\ \mathrm{calories}) $$

Nitrogen Balance

The nitrogen balance (NB) reflects the status of the net protein use:

$$ \mathbf{NB}=(\mathrm{Dietary}\ \mathrm{protein}\times 0.16)-(\mathrm{UUN}+2\;\mathrm{g}\;\mathrm{stool}+2\;\mathrm{g}\;\mathrm{skin})\left( { + 2\;\mathrm{g}\ \mathrm{stool}+2\;\mathrm{g}\ \mathrm{skin}} \right) $$

where

• UUN = urine urea nitrogen

In patients with renal failure, the increased blood urea pool and extrarenal urea losses must be accounted for:

$$ \mathbf{NB}=\mathrm{Nitrogen}\ \mathrm{in}-(\mathrm{UUN}+2\;\mathrm{g}\;\mathrm{stool}+2\;\mathrm{g}\;\mathrm{skin}+\mathrm{BUN}\;\mathrm{change}) $$

Catabolic Index

In addition to the above formulas, the catabolic index (CI) can be derived from the same variables:

$$ \mathbf{CI}=\mathrm{UUN}-[(0.5\times \mathrm{Dietary}\ \mathrm{protein}\times 0.16)+3\;\mathrm{g}] $$

No nutritional stress results in a CI ≤ 0, in moderate nutritional stress CI < 5, and in severe nutritional stress >5.

Creatinine Height Index

Another index of the loss of lean tissue in malnourished patients is the creatinine height index (CHI) and can be calculated as:

$$ \mathbf{CHI}=\mathrm{Measured}\ \mathrm{creatinine}/\mathrm{expected}\ \mathrm{creatinine} $$

Body Mass Index

The body mass index (BMI) normalizes for height and allows comparisons among diverse populations:

$$ \mathbf{BMI}=\mathrm{Body}\ \mathrm{weight}\;(\mathrm{kg})/{{(\mathrm{height})}^2}\;(\mathrm{m}) $$

Harris–Benedict Equation

The Harris–Benedict equation (HBE) is frequently utilized in assessment of the basal energy expenditure [BEE]:

$$ \begin{array}{ll} {\mathbf{HBE}\;\mathbf{BEE}} = {66+(13.7\times (5\times H)-6.8\times A)} {\mathrm{males}} \\ \qquad\qquad\quad\ ={665+(9.6\times W)+(1.7\times H)-(4.7\times A)} {\mathrm{females}} \\ \end{array} $$

where

• W = weight (kg)

• H   =  height (cm)

• A = age (years)

2 Fuel Composition

The body uses different sources of fuel. Table 8.4 depicts some of them:

Table 8.4 Normal fuel composition of the human body

3 Other Formulas

Body Surface Area

The body surface area (BSA) of a patient can be calculated as:

$$ \mathbf{BSA}\;({{\mathrm{m}}^2})=\frac{{{{{(\mathrm{Weight}\;\mathrm{in}\;\mathrm{kg})}}^{0.425 }}\times {{{(\mathrm{height}\ \mathrm{in}\;\mathrm{cm})}}^{0.725 }}\times 71.84}}{10,000 } $$

Ideal Body Weight

The ideal body weight (IBW) for height in males and females can be estimated based on Table 8.5:

Table 8.5 Ideal body weight in males and females

Percentage of Ideal Body Weight

The percentage of ideal body weight (%IBW) is calculated as:

$$ \%\bf{IBW} = \frac{\mathrm{Actual}\ \mathrm{body}\ \mathrm{weight}}{\mathrm{IBW}}\times 100 $$

where

W= actual body weight (kg)