General Principles

General Principles is a topic covered in the Washington Manual of Medical Therapeutics.

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Energy

  • Total daily energy expenditure (TEE) is composed of resting energy expenditure (normally ∼70% of TEE), the thermic effect of food (normally ∼10% of TEE), and energy expenditure of physical activity (normally ∼20% of TEE).
  • It is impossible to determine daily energy requirements precisely with predictive equations because of the complexity of factors that affect the metabolic rate. Judicious use of predictive equations can provide a reasonable estimate that should be modified as needed based on the patient’s clinical course.
  • Malnutrition and hypocaloric feeding may decrease resting energy expenditure to values 15%–20% below those expected for actual body size, whereas metabolic stressors, such as inflammatory diseases or trauma, often increase energy requirements (usually by ∼30%–50% of preillness values).
  • The Harris–Benedict equation provides a reasonable estimate of resting energy expenditure (in kilocalories [kcal] per day) in healthy adults. The equation takes into account the effect of body size and lean tissue mass (which is influenced by gender and age) on energy requirements and can be used to estimate total daily energy needs in hospitalized patients (where W is the weight in kilograms, H the height in centimeters, and A is the age in years).1
    • Men = 66 + (13.7 × W) + (5 × H) − (6.8 × A)
    • Women = 665 + (9.6 × W) + (1.8 × H) − (4.7 × A)
  • Energy requirements per kilogram of body weight are inversely related to body mass index (BMI) (Table 2-1). The lower range within each category should be considered in insulin-resistant, critically ill patients unless they are depleted in body fat.
    Table 2-1: Estimated Energy Requirements for Hospitalized Patients Based on Body Mass Index
    Body Mass Index (kg/m)Energy Requirements (kcal/kg/d)
    1535–40
    15–1930–35
    20–2420–25
    25–2915–20
    ≥30<15

    Note: These values are recommended for critically ill patients and all obese patients; add 20% of total calories in estimating energy requirements in non–critically ill patients.

  • Ideal body weight can be estimated based on height:
    • For men: 106 + 6 lb for each inch over 5 ft
    • For women, 100 + 5 lb for each inch over 5 ft

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