nutritional disorders
Overview of Nutritional Support
Predicting Nutritional Requirements
Nutritional requirements are predicted so that interventions can be planned. Requirements can be estimated by formulas or measured by indirect calorimetry. Indirect calorimetry requires use of a metabolic cart (a closed rebreathing system that determines energy expenditure based on total CO2 production), which requires special expertise and is not always available. Thus, total energy expenditure (TEE) and protein requirements usually are estimated. Total energy expenditure (TEE) varies based on the patient’s weight, activity level, and degree of metabolic stress (metabolic demands); TEE ranges from 30 to 35 kcal/kg/day for people who are sedentary and not under stress to up to 45 kcal/kg/day for people who are critically ill. TEE equals the sum of Resting metabolic rate (RMR, or resting energy expenditure rate), which is normally about 70% of TEE Energy dissipated by metabolism of food (10% of TEE) Energy expended during physical activity (20% of TEE) Undernutrition can decrease RMR up to 20%. Conditions that increase metabolic stress (eg, critical illness, infection, inflammation, trauma, surgery) can increase RMR but rarely by>50%. The Mifflin–St. Jeor equation estimates RMR more precisely and with fewer errors than the commonly used Harris-Benedict equation, usually providing results that are within 20% of those measured by indirect calorimetry. The Mifflin–St. Jeor equation estimates RMR as follows: TEE can be estimated by adding about 10% (for sedentary people) to about 40% (for people who are critically ill) to RMR. For healthy people, protein requirements are estimated at 0.8 g/kg/day. However, requirements may be higher (see table) for the following: Patients with metabolic stress Patients with kidney failure requiring dialysis Patients > 70 years 