Nutritional requirements estimation

TABLE 97-4. Estimating Daily Nutritional Requirements in Adults1,7,19... 

After performing a nutrition assessment and estimating nutritional requirements, determine the optimal route to provide specialized nutrition support (e.g., oral, enteral, or parenteral). If PN is deemed necessary, venous access (i.e., peripheral or central see below) for PN infusion must be obtained. Finally, formulate a PN prescription, and administer PN according to proper safety guidelines. 

Assess the patient s condition to estimate the amount of time he or she is expected to be unable to eat adequately to meet nutritional requirements. If inadequate intake has occurred or is anticipated for 7 to 14 days, start SNS. The threshold for starting SNS is lower for previously malnourished patients than for previously well-nourished patients. 

Patient case A patient s daily nutritional requirements have been estimated to be 100 g protein and 2,000 total kcal. The patient has a central venous access and reports no history of hyperlipidemia or egg allergy. The patient is not fluid restricted. The PN solution will be compounded as an individualized regimen using a single-bag, 24-hour infusion of a 2-in-1 solution with intravenous fat emulsion (IVFE) piggybacked into the PN infusion line. Determine the total PN volume and administration rate by calculating the macronutrient stock solution volumes required to provide the desired daily nutrients. The stock solutions used to compound this regimen are 10% crystalline amino acids (CAA), 70% dextrose, and 20% IVFE. 

Tocopherols (vitamin E) occur in many food substances that are consumed as part of the normal diet. The daily nutritional requirement has not been clearly defined but is estimated to be 3.0-20.0 mg. Absorption from the gastrointestinal tract is dependent upon normal pancreatic function and the presence of bile. Tocopherols are widely distributed throughout the body, with some ingested tocopherol metabolized in the liver excretion of metabolites is via the urine or bile. Individuals with vitamin E deficiency are usually treated by oral administration of tocopherols, although intramuscular and intravenous administration may sometimes be used. 

Based on folate concentrations in liver biopsy samples, and assuming that the liver contains about half of ail body stores, total body stores of folate are estimated to be between 12 and 28 Kinetic studies that show both fast-turnover and very-slow-turnover folate pools indicate that about 0.5% to 1% of body stores are catabolized or excreted daily,suggesting a minimum daily requirement of between 60 and 280)Llg to replace losses. In calculating nutritional requirement, the concept of dietary folate equivalents (DFE) has been used to adjust for the nearly 50% lower bioavailabihty of food folate compared with supplemental folic acid, such that 1 p.g DFE = 0.6 Llg of folic acid from fortified food = 1 j,g of food folate 0.5 p.g foUc acid supplement taken on an empty stomach. Before the fortification program of cereal grains with folic acid conducted between 1988 and 1994, the median intake of folate from food in the United States was approximately 250p.g/day this figure is expected to increase by about 100 Llg/day after fortification. Recommendations... 

Initially, nutrition requirements are determined on the basis of assumptions made about the patient s clinical condition and the nutrition needs associated with repletion or growth, if needed. Once a nutrition intervention has been initiated, periodic reassessment of nutrition status is critical to determine the accuracy of the initial estimate of nutrition requirements. Also, nutrition requirements are dynamic in the setting of acute or critical illness—as the patient s clinical status changes, so will protein and energy requirements, further emphasizing the need for continued reassessment. 

Better markers of nutrition status and methods for determining patient-specific nutrition requirements are needed to allow further refinement of estimates of individual nutrition needs. Functional tests and simple, noninvasive tests for body composition analysis hold promise for the future. However, until better methods of assessment become available clinically and are demonstrated to be cost-effective, the currently available battery of tests will continue to be the mainstay of nutrition assessment. 

It follows that in interpreting observed intake, the intake data must refer to the same time frame as the requirement estimates. Perhaps one of the greatest errors that has been committed by the nutrition community in the assessment of dietary intake is overlooking this dimension and hence overinterpreting one-day dietary data. 

All of the data indicate that some infants do well upon diets which are inadequate for others. The estimates of need may vary nearly 1007o in some instances. It is practically certain that some of this variation is due to the fact that our tools are not very sharp, so a certain but unknown proportion of the discrepancy must be due to error. However, it is most unlikely that all of the variation can be explained in this way and we must conclude that genetic or other factors have very significant effects on nutritional requirements. 

In assessing nutritional requirements, a distinction needs to be made between physiological requirements and dietary requirements. The primary task is to try to estimate physiological requirements that is, the need for the substance or substances within the body for essential metabolic functions. Dietary requirements will normally be greater than this because of the need to take into account the fact that absorption is normally less than 100% efficient and there are subsequent losses in metabolic pathways. 

Generation of data on the nutrient content of agricultural products and foods forms the basis for estimating nutrient intakes of populations via dietary surveys, nutritional labelling for consumer protection, nutrition education for consumer food choice, home and institution menu planning and food purchase, and for research in nutrient requirements and metabolism, toxicant chemical composition is used to assess effects of farm management practices, crop culture, and food processing on chemical content and implications for human health. 

The goal is to transition the patient to enteral or oral nutrition and taper off PN as soon as feasible clinically. When initiating enteral or oral nutrition, monitor the patient for glucose, fluid, and electrolyte abnormalities. Perform calorie counts to determine the adequacy of nutrition via the oral or enteral route. When the patient is tolerating more than 50% of total estimated daily calorie and protein requirements via the oral or enteral route, wean PN by about 50%. PN can be stopped once the patient is tolerating more than 75% of total estimated daily calorie and protein requirements via the oral or enteral route, assuming that intestinal absorption is maintained. 

Estimate kilocalorie and protein requirements of an enteral feeding candidate and design an enteral nutrition (EN) regimen to meet these. 

Ca requirements in the United States are currently set as AIs. The recommended AI for Ca is an approximated value estimated to cover the needs of all healthy individuals in the age group based on experimental or observational data that show a mean intake which appears to sustain a desired indicator of health (e.g., desirable Ca retention) however, lack of sufficient evidence precludes specifying with confidence the percentage of individuals covered by this intake (Standing Committee of the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, and Institute of Medicine, 1997). 

Reference Intakes (DRIs). In the past, the recommended dietary allowances (RDAs), which are the levels of intake of essential nutrients that are considered to be adequate to meet the known nutritional needs of practically all healthy persons, were the primary reference value for vitamins and other nutrients. The DRIs also include other reference values, such as the estimated average requirement (EAR) and the adequate intake (AI). The RDA, EAR, and AI reference standards define nutritional intake adequacy. Since these recommendations are given for healthy populations in general and not for individuals, special problems, such as premature birth, inherited metabolic disorders, infections, chronic disease, and use of medications, are not covered by the requirements. Separate RDAs have been developed for pregnant and lactating women. Vitamin supplementation may be required by patients with special conditions and for those who do not consume an appropriate diet. 

Committees of experts organized by the Food and Nutrition Board of the National Academy of Sciences have compiled Dietary Reference Intakes (DRIs)—estimates of the amounts of nutrients required to prevent deficiencies and maintain optimal health. DRIs replace and expand on Recommended Dietary Allowances (RDAs), which have been published wih periodic revisions since 1941. Unlike the RDAs, the DRIs establish Lpper limits on the consumption of some nutrients, and incorporate the role of nutrients in lifelong health, going beyond deficiency diseases. Boh the DRIs and the RDAs refer to long-term average daily nutrient itakes, because it is not necessary to consume the full RDA every day. 

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