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Section 1 - Nutritional assessment

Nutritional assessment (NA) is the first step in the treatment of malnutrition. Specific data are obtained to create a metabolic and nutritional profile of the patient. The goals of NA are identification of patients who have, or are at risk of developing malutrition; to quantify a patient's degree of malnutrition; and to monitor the adequacy of nutrition therapy.

The initial assessment of nutritional status requires a careful history, a physical examination, and laboratory tests. With the patient assessment in hand, one can then determine the caloric, protein, and fluid needs of the patient.


History

Foremost in nutritional assessment is the patient interview for determining clinical history. Attention should be given to the disease state, duration of illness, intake of nutrients, and presence of such gastrointestinal symptoms as nausea, vomiting, and diarrhea.

Weight loss is often the first clue to an underlying cause of malnutrition. The loss of more than 10% of the patient’s usual weight necessitates a thorough nutritional assessment. Recent unintentional loss of 10% to 20% of the patient’s usual weight indicates moderate protein-calorie malnutrition, and loss of more than 20% indicates severe protein-calorie malnutrition.


Physical Examination

Evaluation of the patient’s overall appearance and thorough physical examination of the skin, eyes, mouth, hair, and nails may provide a clue to the presence of malnutrition.

Weight is one of the most useful elements of the physical examination for the assessment of nutritional status. Body weight is expressed as a value relative to established norms in the general population. Use of these standards may facilitate the diagnosis of significant protein-calorie malnutrition (85% of ideal body weight). The major variable that limits the usefulness of weight and height as indicators of nutritional assessment is water retention, which can occur in many disease states. Fluid retention is a major concern in patients with protein malnutrition as a result of impairments in aldosterone, antidiuretic hormone (ADH), and insulin metabolism.

Anthropometrics are used to estimate subcutaneous fat and skeletal muscle stores objectively. Anthropometric measurements, such as triceps skinfold thickness (TSF) and mid-arm muscle circumference (MAMC), estimate fat and lean tissue mass, respectively. Anthropometry is a useful adjunct in nutritional assessment which is simple, safe, and easily applied at the bedside. Anthropometric data are used in two ways in nutrition assessment:

  • To compare measured values with standardized controls.
  • To compare serial measurements over time in the same patient.

Three anthropometric parameters pertaining to the mid-upper arm are useful in the nutritional assessment of hospitalized adults(16): mid-upper arm circumference (MAC), TSF, and MAMC. They are useful in identifying the most severely malnourished patients, especially those with fluid retention as a result of disease. TSF alone is not a sensitive indicator of malnutrition because many normal adults have less than 5% body fat. However, it is required to calculate MAMC:

MAMC (cm) = MAC (cm) – 3.14 x TSF (mm) ÷ 10 -[(3.14 x TSF (mm)) ÷ 10]

MAMC is easily determined and provides a readily available parameter for nutritional assessment. An MAMC measurement of less than the fifth percentile according to national standards indicates severe protein-calorie malnutrition. An MAMC measurement less then the tenth percentile indicates moderate protein-calorie malnutrition


Labs

Measurements of serum protein levels are used in conjunction with other assessment parameters to determine the patient’s overall nutritional status. Serum proteins used in nutritional assessment include:

  • Albumin
  • Transferrin
  • Prealbumin

Albumin is a complex, high-molecular-weight protein produced by the liver. Because measurement of serum albumin is easy and inexpensive, it is widely used in nutritional assessment. Decreased albumin levels have been shown to correlate with increased morbidity and mortality in hospitalized patients. For this reason it is often used as a prognostic indicator.

Despite the use of serum albumin level as a standard indicator of nutritional assessment, there is some controversy about its sensitivity. The serum albumin level often shows little or no response to nutrition support in the setting of continued sepsis or stress. On the other hand, the serum albumin level changes promptly with refeeding in protein malnutrition if significant stress is not present. Because the serum half-life of albumin is 18 to 20 days and the fractional replacement rate is about 10% per day, in the absence of stress, an improvement in serum albumin level with nutritional repletion is generally observed within 2 weeks. There are other limitations to using the serum albumin level as an indicator of nutritional status. If exogenous albumin is administered, then the serum albumin level loses its predictive value. In addition, certain states of major albumin loss (e.g., severe nephrosis and protein-losing enteropathy) and impaired synthesis (e.g., severe hepatic insufficiency) may limit its usefulness.

Serum transferrin is a beta-globulin that transports iron in the plasma. It has a serum half-life of 7 to 10 days. Serum levels of transferrin are affected by nutritional factors (as are serum levels of albumin during a stress response) and iron metabolism. The shorter half-life of transferrin gives it a theoretical advantage over albumin as a nutritional marker. However, clinical studies do not show any significant difference in their value.

Serum transferrin levels, like albumin, are inversely correlated with the risk or morbidity and mortality in hospitalized patients. One disadvantage is that serum transferrin levels also respond to iron status. High serum transferrin levels are found in patients with iron deficiency. Low levels are found in those with iron overload. Thus, a patient with coexisting iron deficiency and protein malnutrition may have a higher serum transferrin level than another patient with a similar degree of protein malnutrition.

Prealbumin functions in thyroxine transport and as a carrier for retinol-binding protein. Its serum half-life is 2 to 3 days. Measurable changes occur in prealbumin levels within 1 week of a change in nutrient intake. Changes occur more rapidly with metabolic stress.

Disadvantages associated with the use of prealbumin for nutritional assessment include an increased level in renal failure and a failure to respond to malnutrition in the same way as the other secretory proteins (albumin, transferrin, and retinol-binding protein). In addition, the prealbumin level can vary unpredictably with the carbohydrate content of the diet and during metabolic stress.

Immune function
It is well known that malnutrition leads to a decline in immune function. Total Lymphocyte Count is a clinical measure of immune function that is often used in NA. TLC is an indicator of immune function that reflects both B cells and T cells. TLC is calculated using the following equation:

TLC = [% lymphocytes x WBC] / 100

A TLC less than 900 indicates severe depletion, 900 to 1500 is moderate, and 1500-1800 is mild depletion. TLC is increased with infection and leukemia, and decreased following surgery, and in chronic disease states. Because TLC is not specific to nutritional status, it is not useful for assessment of a hospitalized patient.


Estimating energy/calorie needs

To create a tailored nutrition prescription, one must determine the patient's energy/calorie requirements. Indirect calorimetry is the most reliable and readily available method of determining an individual's caloric needs. However, if calorimetry is unavailable, methods to calculate energy requirements are available.

Basal Energy Expenditure
Even in the most physically active people and the most hypermetabolic patients, Basal Metabolic Rate (BMR) or Basal Energy Expenditure (BEE) accounts for the largest portion of total daily energy requirements. BEE is determined largely by body size and body composition. Gender and age also affect BEE. The Harris-Benedict equation is a mathematical formula used to calculate BEE:

Adult males:
BEE (kcal/day) = 66 + (13.7 x wt in kg) + (5 x ht in cm) - (6.8 x age).
Adult females:
BEE (kcal/kcal) = 655 + (9.6 x wt in kg) + (1.7 x ht in cm) - (4.7 x age).

There are more than 100 different variations of the Harris-Benedict equation in the literature. Because of the many conflicting versions of the Harris-Benedict equations and since the major factor which determines BEE is patient weight, some clinicians prefer to use an estimate of 25 kcal/kg for BEE.

Clinical Pearl Harris-Benedict formulas frequently overestimate caloric requirements of hospitalized patients.

Total Energy Expenditure
The next step in determining a patient's energy/caloric needs is to calculate the total energy expenditure (TEE). Surgery, infection, trauma or other stresses to the body add to energy requirements, as does physical activity:

TEE (kcal/day) = BEE x stress/activity factor

Stress or activity level Factor
Bed rest 1.1
Minor surgery 1.1 - 1.3
Ambulatory 1.3
Infection 1.3
Fracture 1.3
Major surgery 1.5
Major trauma 1.7
Sepsis 1.7 - 1.9
Burns 1.9 - 2.1

Calorie sources
Approximately 60 to 80% of the caloric requirement should be provided as glucose, the remainder as lipids. Whether to include protein calories in the provision of energy is controversial. Overfeeding is an increasingly recognized complication of nutritional support. Providing more nutrients than needed may be more harmful than semistarvation. Also, in the hypermetabolic patient with increased energy needs, protein is frequently used for energy.


Fluid requirements

Fluid needs are affected by the patient's functional cardiac, pulmonary, hepatic, and renal status. Fluid requirements increase with fever, diarrhea, hemorrhage, surgical drains, and loss of skin integrity (ie, burns, open wounds). Whereas patients with cardiac, pulmonary or renal disease may require less fluid intake.

The average adult requires approximately 35-45 ml/kg of water per day, the NRC recommends 1 to 2 ml of water for each kcal of energy expenditure. Baseline fluid requirements are determined by the amount of calories administered. Often, meeting the caloric, protein and electrolyte needs of the patient, sufficient, if not excessive, water is provided. Subsequent fluid needs are determined by careful monitoring, particularly:


Protein needs

The average adult requires about 70-80 grams of protein per day, however protein needs may be greatly increased in times of stress. The initial protein goals are estimated according to the following general guidelines.

Stress or activity level Initial protein req
(g/kg/day)
Baseline 1.4
Little stress 1.6
Mild stress 1.8
Moderate stress 2.0
Severe stress 2.2

Subsequent protein needs should be detemined by Nitrogen Balance studies.


Disease State Considerations

The next step is to individualize a patient's nutritional requirements with regard to any concurrent disease states.

Renal insufficiency and ESRD reduces the elimination of nitrogen, produced from the breakdown of protein. Accumulation of nitrogen increases the BUN leading to altered mental status and worsening renal failure. Suggested protein requirements are 0.8-1.0 g/kg/day in patients not receiving dialysis, 1-1.2 g/kg/day in patients receiving hemodialysis and 1.2-1.5 g/kg/day in peritoneal dialysis patients to compensate for actual increases in protein loss into the dialysate solution. Decreased tolerance of carbohydrate and fat substrate is also common since many patients have renal failure secondary to diabetes or cardiovascular disease. Patients may also require decreased amounts of renally eliminated electrolytes (K+ , Mg++, Phos) and acidic anions (Cl-) due to decreased ability of the kidney to reabsorb bicarbonate (HCO3). Fluid restriction may also be necessary in ESRD.

Patients with hepatic insufficiency or failure may have decreased glycogen stores potentially resulting in hypoglycemia and need for increased carbohydrate as a part of their nutritional support. It has been proposed that encephalopathy occurs because of a deceased ability to metabolize aromatic amino acids, which can cross into the brain and act as false neurotransmitters. This theory, and the preferential use of branch-chain amino acids, which are metabolized peripherally, have not been proven.

Respiratory insufficiency such as severe COPD, may necessitate a reduction in the amount of calories given as carbohydrates and a reduction in total fluid volume. Carbon dioxide, a byproduct of carbohydrate metabolism eliminated through expiration, may accumulate and cause increased respiratory drive and respiratory acidosis. Fat produces the lowest amount of CO2 and allows less volume to be given per calorie. Avoidance of over feeding of total calories appears to be just as important and effective at minimizing this complication.


Nitrogen balance studies

Nitrogen Balance (NB) is an important calculation for assessing nutritional response. NB is used to evaluate the adequacy of protein intake as well as to estimate current protein requirements. Nitrogen Balance is a measure of the daily intake of nitrogen minus the daily excretion. NB is determined with the following formula:

Nitrogen Balance = Nitrogen intake – Nitrogen losses

Nitrogen intake = Protein intake (g/day) / 6.25

Nitrogen losses = Urinary Urea Nitrogen (g/day) + 4g*
UUN is determined from a 24 hour urine collection
*4g is a "fudge factor" to account for miscellaneous nitrogen losses

A positive NB indicates an anabolic state, with an overall gain in body protein. Conversely, a negative Nitrogen Balance indicates a catabolic state, with a net loss of protein. With adequate feeding, a Nitrogen Balance between 0 and –5 g/day indicates moderate stress, whereas NB greater than –5 g/day indicates severe stress.


Monitoring response

For nutritional support to be effective, it is necessary to ensure that the nutrients being provided are adequate and are being used properly. It is important to determine whether the goals established in nutritional assessment are being met.

Nitrogen balance may be the most responsive nutritional indicator. Anthropometric measurements are of limited value if performed more frequently than monthly. In the absence of severe stress, serum protein levels change according to their individual half-lives. Thus, improvements in the prealbumin level may occur after 2 to 3 days, and improvements in the transferrin level may occur after 7 to 10 days.

Parameters that are monitored include:


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Section 1 - Nutritional assessment

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