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14
Assessment of Nutritional Status,
Enteral and Parenteral Nutrition,
and the Food Nutrition Label
OBJECTIVES
Upon successful completion of this chapter, the student will be able to:
Assess a patient’s nutritional status based on calculation of body mass
index (BMI) and ideal body weight (IBW).
Perform basic calculations for enteral and parenteral nutrition.
Apply the food nutrition label in related calculations.
Assessment of Nutritional Status
In community pharmacies, pharmacists routinely counsel patients on
matters of nutrition. It is well recognized that poor dietary choices
contribute to obesity and many chronic conditions, including hypertension,
coronary heart disease, sleep apnea, and type 2 diabetes mellitus.1–
3
Furthermore, being extremely overweight, or obese, predisposes one to an
even greater risk of disease, disease complications, and mortality.
Community pharmacists frequently advise patients on general dietary
requirements for the maintenance of good health, provide counseling
regarding weight control, help patients understand the nutritional labeling
on food products, and explain the use and composition of various dietary
supplements. In addition to diet, other factors that can result in obesity
include behavioral, cultural, metabolic, and genetic disposition.
Body Mass Index
The initial phase in managing the overweight or obese patient is an
assessment of the degree of excessive weight. Body mass index is accepted
as the clinical standard for judging excessive weight and obesity. BMI is
defined as body weight in kilograms divided by the square of height
measured in meters. According to the National Institutes of Health (NIH),
2
an individual with a BMI (kg/m2)
≤18.5 (kg/m2) is considered underweight
18.5 to 24.9 (kg/m2) is considered normal
25.0 to 29.9 (kg/m2) is considered overweight
30.0 to 39.9 (kg/m2) is considered obese
≥40 (kg/m2) is considered extremely obese
For an elderly person, a BMI of <21 can be a sign of malnutrition.4 BMI in
most people is an indicator of high body fat; however, this may not be the
case for persons who are especially muscular, such as some athletes.
Determining BMI from a standardized table
BMI may be determined by using a standardized table like that shown in
Table 14.1, in which the intercept of a person’s height and weight indicates
the BMI. Many of the standardized tables available are in units of the
common systems of measurement (i.e., feet/inches and pounds) to facilitate
ease of use by the general public. Others are available in metric or dual
scale.
TABLE 14.1 DETERMINING BODY MASS INDEX (BMI,
kg/m2)
1. Using Table 14.1, determine the BMI for a person measuring 5 feet 8
inches and weighing 160 lb.
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The intercept of 5 feet 8 inches and 160 lb shows a BMI of 24.
2. Using Table 14.1, determine the BMI for a person 183 cm in height and
weighing 96 kg.
The intercept of 72 inches, or 6 feet 0 inches in height and 210 lb,
shows a BMI of 28.
Determining BMI by calculation
If a person’s height and weight are outside the range of a BMI table, or if a
BMI table is unavailable, BMI may be determined by the formula:
1. Calculate the BMI of a person 4 feet 11 inches in height and weighing
98 lb.
2. Calculate the BMI of a person 6 feet 0 inches in height weighing 210 lb.
An alternative formula for the calculation of BMI
BMI may be calculated by the formula:
NOTE: The factor 704.5, used by the NIH, is derived by dividing the square
of 39.37 (inches/m) by 2.2 (lb/kg).
Calculate the BMI for a person weighing 210 lb and standing 72 inches
in height.
Ideal Body Weight
As presented in Chapter 10, a patient’s IBW may be calculated using the
following formulas based on height and gender:
For males:
or, in pounds
For females:
or, in pounds
A patient’s actual body weight (ABW) can be compared with his or her
IBW to assess nutritional status as shown in the next section5:
ABW ≤ 89% IBW is considered underweight.
ABW 90% to 120% IBW is considered normal.
ABW > 120% to <150% IBW is considered overweight.
ABW ≥ 150% to <200% IBW is considered obese.
ABW ≥ 200% IBW is considered extremely obese.
Calculation of IBW and comparison of ABW
1. Calculate the IBW (in pounds) for a male patient who is 6 feet tall and
weighs 210 lb, determine the percentage of his ABW compared to his
IBW, and indicate the nutritional category into which he falls
according to his weight.
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Because his ABW is between 120% and 150% of his IBW, he falls into
the “overweight” category.
2. Calculate the weight range in pounds for a female patient who is 5 feet
4 inches tall to fall within the “normal” nutritional category based on
her IBW.
Considerations in Parenteral and Enteral
Nutrition
Pharmacists are increasingly involved in providing enteral and parenteral
nutrition services in the institutional as well as in the home care setting. In
this role, pharmacists may take part in the selection of the nutritional
formula, prepare the product for use, and/or participate in its administration.
Figure 14.1 depicts the three routes of nutrition: oral, enteral, and parenteral.
FIGURE 14.1 Routes of nutrition: oral, enteral, and parenteral.
The content provided in this chapter is introductory. Pharmacists’ actual
participation in providing parenteral and enteral nutrition services requires a
comprehensive understanding of all aspects of this specialized field.
Practice guidelines and critical reports are provided by the American Society
for Parenteral and Enteral Nutrition (ASPEN); its publication, Journal of
Parenteral and Enteral Nutrition; and its web site,
http://www.nutritioncare.org.
The following points are emphasized within the context of the limited
scope of this chapter:
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The order form for parenteral nutrition presented by Figure 14.2 is an
example. Such forms and their content vary between institutions.
Nutritional orders are individualized for each patient based on age,
metabolic condition, organ function, disease state, and medication
usage.
Calculations are often performed to provide the “targets” for nutritional
components, which then may be rounded or modified based on
individual patient requirements.
The most common errors associated with parenteral nutrition involve
dosage formulation, dosage calculations, and infusion rates.
6
Standard units of measure used are grams for the base components
(i.e., dextrose, amino acids, and lipids), milliequivalents for
electrolytes, and millimoles for phosphate, all in a specified volume, as
per liter, or volume for a 24-hour infusion. The rate of flow is stated in
milliliters per hour for a designated period of time, usually 24 hours.
Parenteral and enteral nutrition orders should be clearly labeled with
all identifiers of the patient, formula and quantity, route and rate of
administration, infusion time, expiration date, and, for enteral
preparations, the statement “Not for I.V. Use.”
6
FIGURE 14.2 Example of part of an order form for adult
parenteral nutrition.
Enteral Nutrition
Enteral nutrition is a method of providing nutritional support via tubes
inserted into the stomach or small intestine. It finds application in patients
who have an inability or decreased ability to ingest nutrients by mouth. As
shown in Figure 14.1, nasogastric tubes may be used, or tubes may be
inserted through surgical openings into the stomach, duodenum, or
jejunum.7 Surgical insertions generally are reserved for the relatively longterm feeding requirements of patients (e.g., more than 4 weeks). Enteral
nutrition may be used for total nutrition, for supplemental nutrition, or as a
transitional phase for patients transitioning from parenteral nutrition. Tube
feedings may be intermittent or continuous, and in addition to nutritional
requirements, they address the need to replace water lost daily through
urination, bowel function, respiration, and perspiration.
Enteral nutrition takes into account a patient’s caloric requirements and
his or her need for protein, carbohydrate and fat, vitamins and minerals,
dietary fiber, electrolytes, and fluids. Commercial formulas for enteral
feeding are multiple and varied. Some are designed specifically for pediatric
or adult patients. Some provide a balanced or general requirement; others
are high in calories, protein, fat, and/or fiber; and still others are low in
carbohydrate, sodium, or cholesterol. Some commercial formulas are
designed to meet the disease-specific requirements of certain patients, such
as those with renal or hepatic disease or those who are diabetic, lactose
intolerant, or allergic to specific foods. As required, additions may be made
to commercial formulas to meet the needs of a specific patient.
The osmolality of an enteral formula is an important consideration.
Some patients exhibit intolerance to a hyperosmolar formula, resulting in
vomiting, osmotic diarrhea, abdominal distention, and other symptoms.
8
Most infant formulas have osmolalities between 150 and 380 mOsmol/kg,
and adult formulas from about 270 to 700 mOsmol/kg. It should be recalled
that the osmolality of extracellular fluid is considered to be 285 to 295
mOsmol/kg.
When necessary, medications can be administered through the enteral
feeding tubes, preferably as liquid dosage forms. As required, well-diluted
slurries can be prepared and administered from the solid contents of tablets
or capsules. Liquid medications with high osmolalities (some are >1000
mOsmol/kg) can be diluted with 10 to 30 mL of sterile water prior to
administration.7,
9
Medications generally are administered separately from the nutrient
formulas, with care taken not to conflict with the feeding schedule, to avoid
drug incompatibilities with other medications and nutritional components;
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to consider a medication’s possible gastrointestinal effects (e.g., diarrhea or
constipation); and to make certain that no residual medication remains in the
feeding tubes after medication delivery.7,
9
Parenteral Nutrition
Parenteral nutrition (PN) or intravenous hyperalimentation (IVH or
HAL) is the feeding of a patient by the intravenous infusion of fluids and
basic nutrients. Partial parenteral nutrition (PPN) is nutritional support
that supplements oral intake and provides only part of daily nutritional
requirements. Total parenteral nutrition (TPN) provides all the patient’s
daily nutritional requirements.
Parenteral nutrition is used for patients who cannot obtain adequate
nutrition by oral means. This includes patients who are severely
malnourished, those whose critical illness temporarily precludes their
receiving oral or enteral nutrition and there is need to prevent starvationinduced complications, those whose gastrointestinal tracts are unavailable or
malfunctioning, those with a demonstrated or assessed probability of
ineffective nourishment by enteral feeding, and patients in renal or hepatic
failure, among others.10,
11
Figure 14.2 is an example of a hospital adult parenteral nutrition form.
Note that the prescribing physician may select the standard formulas or
modifications for central or peripheral administration. In the example, the
quantities of the basic components, amino acids (protein), dextrose
(carbohydrate), and lipid (fat), are expressed in percent strength; however,
other such forms may express these quantities in grams per stated volume.
Added electrolytes are expressed in milliequivalents and phosphorus in
millimoles. The patient’s dosing weight (the actual, ideal, or adjusted body
weight) is used to determine the component doses. Central administration
lines are inserted into the superior vena cava, whereas peripheral lines are
inserted into veins of the arm or hand (see Fig. 14.1). Because concentrated
dextrose solutions are hypertonic and may be damaging to veins, central
lines are preferred over peripheral lines for higher concentrations of
dextrose (e.g., 25%). Nutritional formulas for peripheral parenteral nutrition
generally are isotonic or near isotonic.
Typically, parenteral nutrition formulas contain the following:
Macronutrients:
Carbohydrate (e.g., dextrose)Protein (e.g., amino acids)Fat (e.g., lipid
emulsions)
Micronutrients:
ElectrolytesVitaminsTrace elements
Sterile water for injection
Parenteral nutrition formulas can be obtained commercially or they may be
prepared in the pharmacy, often through the use of automated compounding
devices that mix the basic as well as additive ingredients according to input
managed by computer software. Nutritional requirements and thus
formulations differ based on age groups (e.g., neonates, general pediatrics,
adults) as well as patient-specific diseases (e.g., renal, liver, pulmonary). In
preparing formulas for parenteral nutrition, pharmacists use calculated
quantities of small-volume parenterals (ampuls and vials) as the source of
electrolytes, vitamins, and minerals, and large-volume parenterals (LVPs) as
the source of amino acids, dextrose, lipids, and sterile water for injection.
Typically, infusion rates are begun at about 25 to 50 mL/h and adjusted
every 8 to 12 hours as dictated by the patient’s condition and fluid and
nutritional status.11 TPN solutions may be administered continuously over a
24-hour period or cyclically, depending on a patient’s requirements.
Infusions are administered through the use of automated, high-speed
multichannel pumping devices.
In many instances, parenteral nutrition begun in a hospital is continued
in a long-term care or rehabilitation facility or in home care.
Nutritional Requirements
Nutritional requirements are the quantities of macronutrients and
micronutrients needed for a patient to obtain or maintain the desired
nutritional status. The quantitative amounts of fluid and specific nutrients
required vary with an individual’s age, gender, physical parameters, disease
state, and current nutritional status. The purpose of this section is to provide
only general considerations. More detailed and patient-specific
considerations are presented in other resources, including those
referenced.5,6,9–
15
Fluid requirements
Total body water in adult males normally ranges between 50% and 70% of
body weight depending on the proportion of body fat. The greater the
proportion of fat, the lesser the proportion of water. Values for adult women
are about 10% less than those for men. Of the adult body’s water content, up
to two-thirds is intracellular and one-third is extracellular. For an adult,
approximately 2500 mL of daily water intake (from ingested liquids and
foods and from oxidative metabolism) is needed to balance the daily water
output.
16
Factors of 30 to 35 mL/kg of body weight, 1500 mL per square meter of
body surface area, or 1 mL/kcal of nutrition required are among the methods
used to estimate an adult patient’s daily fluid or water requirement. On a
case-by-case basis, these values may be increased (e.g., for patients who are
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