If you want to maintain energy balance, it is necessary to contribute energy expenditure. There are two basic methods for estimating calorie needs.
One is the use of the Harris-Benedict equation (or any other available equation), the other is the analysis of the aspirated gases (see the indirect calorimetry section).
The Harris-Benedict equation is derived from a population analysis and takes into account the patient’s age, sex, height, and weight. The number calculated is the basal energy expenditure (BEE) which is the energy expended during rest in a stress-free state after an overnight fast.
In the presence of metabolic stress (table 9) during which energy demands are increased, the BEE must be multiplied by a stress factor in order to obtain an adequate estimate of energy needs (table 10).
The equations are:
Men: BEE = 66 + (13.7 x weight)
+ (5.0 x height) – (6.8 x age)
Women: BEE = 655 + (9.6 x weight)
+ (1.7 x height) – (4.7 x age)
Weight = Weight in kg.
Size = Size in cm.
Age = Age in years.
Table 9. Classification of stress by categories.
*In the absence of diabetes, pancreatitis or steroid therapy. Adapted from Cerra FB. A Pocket Manual of Surgical Nutrition. CV Mosby Co., St. Louis, 1984 p. 43.
Table 10. Guide for determining nutritional requirements based on the level of metabolic stress.
BEE = Basic energy requirement; CNP = Non-protein calories; N = Nitrogen; AA = Amino acids; CHO = Carbohydrates.
Adapted from Cerra FB. A Pocket Manual of Surgical Nutrition. CV Mosby Co., St. Louis, 1984. p. 60.
The BEE is easy to use, does not require sophisticated technical equipment and allows calculations to be carried out quickly and without much cost.
However, it is not necessary in the presence of metabolic stress. The REE is quite accurate in most clinical situations.
It measures oxygen consumption, which can be used to determine the degree of hypermetabolism and to measure RQ so that combustion can be monitored and the administration of excess calories and glucose can be avoided.
This measurement, requiring advanced technology and enormous work, is expensive and cannot be easily used in various clinical situations such as when inspired oxygen concentrations above fifty percent are used in intubated patients or when the inspiratory fraction of oxygen is greater than 20 % in non-intubated patients.(1,3,7)
In both cases the values are estimates of energy expenditure and allow a rational start of the nutritional contribution. Needs should be monitored based on response and results in order to tailor the appropriate regimen for the patients’ particular needs.
Glucose needs
In states of starvation, non-protein calories can be supplied as glucose alone or as some combination of glucose and exogenous fat.
In the first case, lipids should be provided only in sufficient quantities to prevent the deficiency of essential fatty acids. In the latter case, fats are provided as a caloric source along with glucose.
If glucose is supplied in excess of demand or if total calories are given in excess of demand, lipogenesis occurs, the RQ exceeds 1.0, minute ventilation increases, hepatic steatosis occurs, and excretion increases. of catecholamine significantly.
There is a direct linear relationship between glucose load and CO2 production.
Through isotope studies the maximum usable glucose load appears to be 5 mg/kg/min. In general, a non-protein intake of 20 to 25 kcal/kg/day is a reasonable estimate. The ratio of non-protein calories per gram of nitrogen administered is approximately 150:1.
In diabetes, calories from glucose can be substituted for fat with a resulting reduction in glucose intolerance.(1)
Fraction of energy expenditure
In states of stress, BEE increases and total glucose oxidation also increases, but the fraction of total energy expenditure derived from glucose decreases.
Even though glucose production is increased and peripheral uptake is normal, glucose entry into the Krebs cycle is reduced and is recycled as lactate and pyruvate.
Furthermore, exogenous glucose does not very efficiently reduce the rate of gluconeogenesis.
For this reason, the glucose load must be reduced and the difference in calories must be completed with lipids.(1,7)
Grease requirements
The intravenous lipid preparations currently available in the United States are emulsions of triglycerides and essential fatty acids.
They are used in nutrition and metabolic support to prevent or treat deficiencies of essential fatty acids.
In starvation states it is necessary to give a certain amount of essential fatty acids to prevent essential fatty acid deficiency.
These requirements are also necessary as a consequence of the inhibition of lipolysis due to the insulin response to high glucose infusions.
In stress situations, plasma changes with a deficiency of essential fatty acids (decrease in arachidonic acid and increase in oleic acid) have been observed, present since the beginning of stress, probably as a reflection of changes in the hormonal environment.
Exogenous fat emulsions are effective in combating this problem and are also effective as a caloric source. They have also been shown to have a protein-sparing effect equivalent to that of glucose.
Therefore, lipids can be used to supply up to 30% of caloric requirements.
However, due to the immunosuppressive effects of high doses of polyunsaturated fatty acids, it is best to limit intravenous lipid emulsions to less than 1 g/kg/day (Table 10).(1,7)
Protein requirements
With the onset of starvation, glucose becomes the main fuel for energy production. When glycogen stores are rapidly depleted, amino acids become the primary carbon source for hepatic and renal glucose production.
The source of amino acids is the mobile depot of amino acids located in the muscle in the connective tissue and in the viscera.
After several days, an adaptation process occurs whose basic principle is to save amino acid deposits by replacing glucose with other destined carbon sources, thereby reducing the loss of lean body mass with a reduction in urinary nitrogen excretion.
The sources of this carbon reside mainly in mobilized fat and in the production of ketone bodies by the liver. Furthermore, the oxidation of glucose is reduced and it is recycled as lactate while glycerol is transformed into an available source for gluconeogenesis.
During starvation both glucose and exogenous fat lead to a reduction in amino acid mobilization. If amino acids are supplemented along with vitamins, electrolytes, minerals and trace elements it is possible to achieve a positive nitrogen balance and a positive caloric balance, especially if these measures are associated with an exercise program.
With the activation of mediator systems the synthesis of body protein:
It decreases and hepatic protein synthesis increases as a consequence of the production of acute phase reactants. Catabolism increases with an increase in the oxidation of amino acids as a source of energy and in the mobilization of amino acids from the periphery.
The rate of total body protein synthesis can be increased by the administration of exogenous amino acids.
It can be achieved with the metabolic rate phenomenon reflected by reaching an equilibrium in the nitrogen balance (2 to 4 g of positive nitrogen balance).
Reducing the absolute rate of catabolism by administering exogenous amino acids appears to be relatively ineffective. Increasing the amino acid load beyond this equilibrium point appears to increase both the rate of anabolism and catabolism without a significant change in equilibrium.
The amino acid load necessary to meet the demands of energy production and protein synthesis and to achieve nitrogen balance increases with the amount of metabolic stress present (Table 10).(1,7)
Fluid requirements
Normal fluid requirements for adults are 1,500 to 2,500 ml/day. On average patients require 30 ml/kg of body weight. The fluid requirement of an individual patient may be greater in the presence of extrarenal fluid losses such as those that occur in fever, excessive sweating, in fistulas and wound drainage, and in vomiting and diarrhea. In these cases, additional fluids must be provided either orally, through nutrition tubes and by intravenous infusion (table 11).(3)
Table 11. Daily basal fluid requirements for adults.
Taken from Randall HT. Fluid, electrolyte, and fluid base balance.
Surg Clin North A 1976; 56: 1019-1058.
Conclusion
An ideal test for the assessment of nutritional status should be highly sensitive and specific, should not be affected by factors unrelated to nutrition, and should correlate adequately with the response to nutritional repletion.
Given the lack of sensitivity, specificity and independence of most of the parameters described in this article, the design of a clinically useful approach with an adequate cost-benefit ratio for the assessment of nutritional status is a challenge.
Better indices of nutritional status are definitely required.
Bibliographic references
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- 2. Strausburg KT. Nutrition/metabolic assessment. In Strausburg KT, Cerra FB, Lehmann S, Shronts EP (Eds.). Handbook for Nutrition Support. Harvey Whitney Publishers, 1992.
- 3. Hopkins B. Assessment of nutritional status. In Gottschlich M, Matarese L, Shronts EP (Eds.). Nutrition Support Dietetics Core Curriculum, 2nd edition. ASPEN 1993.
- 4. Shronts EP. Nutritional assessment in hepatic failure. Nutr Clin Prac. 1988; 3(3): 113-119.
- 5. Ireton-Jones CS, Hasse JM. Comprehensive nutritional assessment: The dietitian’s contribution to the team effort. Nutrition. 1992; 8(2): 75-81.
- 6. Teasley-Strausburg KM, Anderson JD. Assessment, prevalence, and clinical significance of malnutrition. In Dipiro JT, Talbert RL, et al (Eds.). Pharmacotherapy: A Pathophysiological approach. 2nd ed., Appleton & Lange, Norwalk, CN 1993.
- 7. Shronts EP, Lacy J. Metabolic support. In Gottschlich M, Matarese L, Shronts EP (Eds.). Nutrition Support Dietetics Core Curriculum, 2nd edition ASPEN, 1993.
- 8. Daley BJ, Bistrian BR. Nutritional assessment. In: Zaloga GP (ed.): Nutrition in Critical Care. CV Mosby Publishers, 1994.
- 9. ADA’s definitions for nutrition screening and nutrition assessment. J Am Diet Assoc. 1994; 94(8): 838-39.