Estimating Energy Needs in Nutrition Support Patients

Abstract

D etermination of energy needs is a cornerstone of all nutrition support prescriptions. Daily energy expenditure consists of the resting metabolic rate, diet-induced thermogenesis, and physical activity. In sick individuals, the resting metabolic rate is sometimes increased, but the physical activity is usually reduced. The increase due to hypermetabolism and the change in physical activity can be highly variable.Scores of studies have been published describing the metabolic rate of numerous types of patients.1-8 However, in this field of study, the large volume of data seems to increase rather than decrease uncertainty as to how to make the metabolic rate determination. Among the questions often asked are, which equation, which body weight, which stress modifiers, and which activity modifiers measure or estimate? In this article, each of these questions will be addressed and, where possible, answered. Measurement of Metabolic RateThere is no question that measurement of metabolic rate is the most accurate way to determine energy requirements, and indirect calorimetry is by far the most common way to perform the measurement. 9 Indirect calorimetry is the measurement of pulmonary gas exchange (oxygen consumption and carbon dioxide production). The method relies on the fact that the amount and mixture of carbohydrate, fat, and protein being oxidized by the body produce a specific amount of heat and carbon dioxide and consume a specific amount of oxygen. At a given ratio of carbon dioxide production to oxygen consumption (ie, respiratory quotient), each gas has an associated constant heat equivalent. Thus, the measurement of gas exchange allows a reliable calculation of metabolic rate. Technically, the amount of nitrogen lost should also be determined from analysis of the urine, but it has been shown that ignoring the nitrogen loss produces only a small error in the result. 10In conducting an indirect calorimetry measurement, it must be remembered above all that this is a respiratory measurement that only reflects metabolism reliably if proper conditions are maintained. Hypoventilation or hyperventilation will alter the apparent carbon dioxide production.9 Air leaks will affect both the apparent oxygen consumption and carbon dioxide production. Loss or gain of carbon dioxide during acid base disturbances and inspired oxygen concentrations Determination of energy needs is a fundamental part of nutrition support. The amount of metabolically active tissue mass is the major determinant of metabolic rate. The other components of total energy requirement in an adult are physical activity, dietinduced thermogenesis, and illness hypermetabolism. Measurement with indirect calorimetry is possible but not common. Measurement can capture the effect of body size, dietinduced thermogenesis, and illness on metabolic rate but usually not the effect of physical activity. More often, the energy need is calculated based on its association with body weight and composition. Many equations have been proposed over the years, as have adj...

Assessment of the Patient

“…The major determinants of metabolic rate are (1) the amount of metabolically active tissue mass, (2) the effect of physical activity, (3) diet induced thermogenesis and (4) illness hypermetabolism. Together, these comprise the total daily energy consumption [ 84 ]. Indirect calorimetry (IC) is considered the gold-standard method for establishing energy expenditure in the clinical setting, and its use is recommended in guidelines, particularly for patients with severe malnutrition, obesity, or infl ammatory states where there is less correlation between measured energy expenditure and commonly used predictive equations [ 67 ].…”

Do Patients in the Intensive Care Unit Receive Recommended Total Daily Calories with Enteral Feedings Using a Rate Based Protocol?

“…Nutritional needs are calculated by determining a patient's daily energy requirements (Frankenfield & Ashcraft, 2011). This is calculated by determining daily energy expenditure, which consists of physical activity, resting metabolic rate, and dietinduced thermogenesis.…”

“…Jeor for healthy patients and the Swinamer, Penn State equation or Brandi for critically ill patients (Frankenfield & Ashcraft, 2011). Which standard equation used may be determined by the individual facility, however they all will calculate a patient's daily nutritional needs.…”

Resting energy expenditure in critically ill patients: Evaluation methods and clinical applications

“…It is not commonly used in hospitals. 40 IC is considered the gold standard for measuring REE in critically ill patients, 41,42 and measurement is based on gas exchange, with energy production from the consumption of oxygen (O 2 ) and production of CO 2 . It is estimated that approximately 80% of EE is due to O 2 consumption, while the remaining 20% are attributed to EE due to CO 2 production.…”

“…67,68 The Penn State University equation is the most exact and precise indicator of REE in the critically ill patients, and should be used when IC is not feasible, combined or not with the rule of thumb in order to improve precision. 42,61,69,70 IC is the best technique to ensure exact determination of EE and consequently the ideal nutritional intake, and thus should be use whenever possible in critically ill patients.…”