EVALUATION OF NUTRITION

EVALUATION OF NUTRITIONAL STATUS

Height and weight measurements are probably the most important set of vital signs in nutritional assessment.

HEIGHT

A patient's height is the key component in the determination of IBW. (See information below on the determination of IBW using one of three methods). No matter which calculation method is used, IBW needs to be adjusted for frame size, spinal cord injury (SCI), and amputation, as follows:

• Frame size

  • Small frame size - Decrease IBW by 10%

  • Medium frame size - No changes needed in IBW

  • Large frame size - Increase IBW by 10%

• SCI

  • Paraplegia - Decrease IBW by 10-15 lbs

  • Tetraplegia - Decrease IBW by 15-20 lbs

• Amputation

  • Hand - Decrease IBW by 7%

  • Forearm and hand - Decrease IBW by 2.3%

  • Total arm - Decrease IBW by 4.9%

  • Foot - Decrease IBW by 1.5%

  • Calf and foot - Decrease IBW by 5.8%

  • Total leg - Decrease IBW by 16%

METHODS OF CALCULATION

• Hamwi calculation - This method is appropriate for patients aged less than 65 years and has been adjusted for gender.

  • Males

    • 106 lbs for the first 5 feet and 6 lbs per inch thereafter

    • Example - 5'10" = 166 lbs

  • Females

    • 100 lbs for the first 5 feet and 5 lbs per inch thereafter

    • Example - 5'10" = 150 lbs

• Metropolitan scale (1959)

  • Weights were obtained from approximately 5 million healthy life insurance policyholders who were tracked by insurance companies for approximately 20 years.

  • Frame sizes were not measured in any subject.

  • Weights associated with the greatest longevity were assigned to the medium frame category.

• Geriatric Weight Scale - This scale is for patients aged more than 65 years. It has been adjusted from the stringent weight recommendations of the Metropolitan scales to accommodate an aging population.

WEIGHT

Body weight at admission is probably the most reliable weight when determining a patient's actual body weight, assuming that weight is a dry body weight. Weight status becomes an unreliable measure postoperatively or during an acute crisis, because of the administration of fluids or the development of an edematous state. As a chronic marker, one can assume that a weight gain or loss is related to an increase or decrease in lean body mass.

• To determine the weight to use for feeding calculations, first derive a figure by calculating the percentage of IBW.

  • Percentage IBW = (actual body weight [ABW]/IBW) x 100

    • If ABW is less than IBW, use ABW to determine nutritional needs.

    • If ABW is greater than IBW but less than 120%, use IBW to determine nutritional needs.

    • If ABW is greater than IBW and more than 120%, use the adjusted or relative body weight to calculate needs: IBW + (ABW – IBW x 0.25).

The following scale presents categories of the nutritional status of patients, using ABW as a percentage of IBW:

v  More than 200% of IBW = Morbidly Obese

v  More than 150% of IBW = Obese

v  More than 120% of IBW = Overweight

v  100% of IBW +/- 10% = Normal

v  80-90% of IBW = Mild Malnutrition

v  70-80% of IBW = Moderate Malnutrition

v  Less than 70% of IBW = Severe Malnutrition

The BMI is a very practical and useful measurement that allows easy determination of categories of weight status.

WEIGHT CLASSIFICATIONS

PROTEIN STATUS

Measurements of visceral and somatic protein status are biochemical indices used to evaluate nutritional status.

Visceral protein parameters include albumin, transferrin, and prealbumin. According to Charney, serum albumin is perhaps "the most studied biochemical parameter used in nutrition screening and assessment."

Albumin is an osmotic protein that constitutes 40% of the total body protein pool of 4-5 g/kg and is maintained largely in the intravascular compartment, with the remainder distributed in extravascular tissues. The serum albumin level is not a definitive measure of visceral protein status, but it reflects the complex relationship between synthesis, degradation, and distribution.

Key albumin levels are distributed as follows:

• Normal levels are 3.5-5.0 g/dL.

• A level of 3.0-3.5 g/dL is considered to be a nutritional decision point, or a point when nutritional intervention should be considered or adjusted.

• Levels that are less than 3.5 g/dL have been correlated with poor surgical outcome, unfavorable prognosis, increased cost of hospitalization, and prolonged intensive care unit (ICU) stay.

• Levels that are less than 3.0 g/dL are often associated with severe malnutrition.

• Levels that are less than 2.5 g/dL are associated with increased rates of morbidity and mortality.

Albumin does have limitations as a nutritional marker because of its lengthy half-life of 21 days and the numerous factors that decrease albumin levels, independent of nutritional status.

Non-nutritional factors that affect albumin levels include the following:

Ø  Inadequate synthesis, as seen in cirrhosis, some cancers, acute stress, congestive heart failure, and hypoxia

Ø  Impaired digestion, as seen in pancreatic insufficiency and malabsorption

Ø  Altered fluid status, such as that found in edematous condition and overhydration

Ø  Chronic protein loss, as found in nephrotic syndrome and with burns

Because of its long half-life, serum albumin cannot be used effectively for monitoring acute response to nutritional therapy. Albumin levels should be included on the initial chemistry profile for nutritional screening purposes and monitored during hospitalization for visceral protein repletion trends or as a chronic marker for nutritional status.

Owing to its shorter half-life (8-9 d) and smaller body pool size, transferrin makes a better nutritional marker of visceral protein status than does albumin.

Normal levels of transferrin range between 200-400 mg/dL, and a level of 150 mg/dL is considered a nutritional decision point or a point when nutritional support should be considered or adjusted.

Transferrin levels are decreased in the following situations:

v  Impaired synthesis, which can result, for example, from acute fasting, chronic infection, or pernicious anemia

v  Increased excretion, as with nephritic syndrome, inflammation, burns, and liver damage

v  Overhydration

v  Increased iron stores, as with hemosiderosis and hemochromatosis

Transferrin levels are increased in the following situations:

• Decreased iron stores, as with iron deficiency anemia and chronic blood loss

• Increased protein synthesis, which is seen in estrogen therapy and oral contraceptive use

• Dehydration

• Pregnancy – 2nd and 3rd trimesters

The serum concentration of transferrin is about 0.8 times the total iron binding capacity (TIBC). If the direct measurement of transferrin is not possible because of the high cost and limited availability of the equipment needed, the transferrin level can be easily calculated from the TIBC, using the following formula:

• TIBC x 0.8 – 43 = Transferrin

The third measure of visceral protein is prealbumin, which is synthesized in the liver and catabolized in the kidney. Prealbumin has a small total body pool and a very short half-life (2 d), making it an excellent nutritional marker. Prealbumin has been used increasingly as a marker of response to nutritional therapy.

Reference range values for prealbumin are from 16-35 mg/dL. A nutritionally significant value of prealbumin is 11 mg/dL. A value below this level signifies malnutrition. The failure to increase prealbumin above 11 mg/dL with nutritional therapy is an indication that nutritional needs are not being met. Concentrations should increase nearly 1 mg/dL daily or should double in a week when adequate therapy is being provided.

Non-nutritional factors that decrease prealbumin include the following:

• Stress

• Inflammation

• Surgery

• Cirrhosis

• Hepatitis

• Renal failure

Table 2 summarizes the 3 visceral proteins in relation to the degree of malnutrition.

DEGREE OF MALNUTRITION

Somatic protein measurements include the CHI and nitrogen balance studies. Protein status can be assessed biochemically by using the CHI, which measures the 24-hour urinary creatinine excretion and compares it to an ideal value based on ideal weight for height.

NITROGEN BALANCE STUDIES

Nitrogen balance studies measure the net change in the body's total protein. An estimate of nitrogen balance can be obtained by measuring urinary urea nitrogen (UUN) and comparing it to nitrogen intake during that same time.

• Nitrogen balance is calculated as follows: N2 balance = N2 intake – N2 excretion Or = [protein (gm)] – (24 hour UUN + 3)

• [6.25 gm nitrogen]

• A "fudge factor" of 3 is added to account for the insensible nitrogen losses in the feces, skin, and drainage of body fluids.

If calculated nitrogen balance equals the following:

• Nitrogen balance = 0

  • This signifies nitrogen balance.

  • Healthy adults usually are in nitrogen balance.

• Nitrogen balance >0

  • A positive nitrogen balance is indicated.

  • Protein anabolism exceeds protein catabolism.

  • This is usually seen with pregnancy, growth, and recovery from illness and/or nutritional repletion.

  • The goal in nutritional repletion is a positive nitrogen balance of 4-6 grams per day.

• Nitrogen balance <0

  • Negative nitrogen balance

  • Protein catabolism exceeds protein anabolism

  • Observed in situations of starvation, increased catabolism resulting from trauma or surgery, and inadequate nutrition therapy

HEMATOLOGICAL MEASUREMENTS

Serum hemoglobin and hematocrit may reflect a generalized state of malnutrition. As with the visceral and somatic visceral proteins, non-nutritional factors (eg, blood loss, chronic infection, and overhydration) must be considered as a potential etiology of decreased serum concentrations.

MALNUTRITION

The determination of malnutrition can be categorized using the following definitions:

Ø  Marasmus - This term refers to a typical starved patient.

o    Malnutrition is characterized by the following:

§  Deficiency in total calorie intake

§  Preservation of visceral protein production

§  Depletion of somatic protein (skeletal muscle and adipose stores)

§  Impairment of cell-mediated immunity and muscle function

Ø  Kwashiorkor - This is a typical hypermetabolic or catabolic patient.

o    Malnutrition is characterized by the following:

§  Adequate calorie intake but deficient protein

§  Depletion of visceral protein pools

§  Some depletion of somatic protein with relative preservation of adipose tissue

§  Possible impaired immune function

Ø  Protein/calorie malnutrition - This typically is a marasmic patient who becomes hypermetabolic or catabolic. This could also occur in circumstances where there is a decreased oral intake of food for a prolonged period of time.

o    Malnutrition is characterized by the following:

§  Depletion of visceral protein pools

§  Depletion of somatic protein and adipose tissue

§  Reduced immunocompetence that may be caused by such factors as a global decrease in body protein, including globulins, and a decreased production of T-lymphocytes. The exact relationship between nutritional status and immunity in hospitalized patients has not yet been fully explained.