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 Daily energy requirements are calculated based on the patient’s ideal body weight (IBW) (Table. 7.1). Adjusted body weight is used if the patient’s weight exceeds IBW by 20%. If the patient’s weight is less than 90% of IBW then the actual weight is utilized.

 The estimated daily energy consumption used to determine total energy requirements is 25 kcal/kg/day. In obese patients with a body mass index (BMI) >30, energy requirements are decreased to 22 kcal/kg/day.

 The amount of protein is determined by factors including severity of illness, surgical trauma, and organ system failure (Table 7.2). This allows the protein intake to be matched to the body’s synthetic requirements. At the same time, the calories contributed by the proteins are counted towards the total energy requirements, to minimize the risk of overfeeding.

 Half the total caloric requirements are supplied by carbohydrate. The remaining half of caloric requirements is divided between lipids and proteins in a ratio determined by the patient’s protein requirement. The amount of each component is calculated using the energy equations (Tables 7.3 and 7.4).

Table 7.1 Determining patients’ ideal body weight (IBW).*

Males IBW = 48 kg for the first 5 feet of height + 2.7 kg for each inch taller

Females IBW = 45.5 kg for the first 5 feet of height + 2.2 kg for each inch taller

For patients with actual weight greater than 1.2 times IBW the adjusted body weight (ABW) is used ABW= ([actual weight – IBW] × 0.25) + IBW

For patients with actual weight less than 0.9 times IBW the actual body weight is utilized

^* G. J. Hamwi Formula (1964).

Table 7.2 Determining protein requirements (g/day).

Physiologic stress, post‐surgery, or wound healing =1.2–2.0 g/kg/day × [weight in kg*]

Critical illness = 1.5 g/kg/day × [weight in kg]

Renal failure, not on renal replacement therapy = 0.8–1.2 g/kg/day × [weight in kg]

Hemodialysis = 1.2–1.4 g/kg/day × [weight in kg]

Continuous veno‐venous hemofiltration ≥1.5 g/kg/day × [weight in kg]

^* Weight determined from Table 7.1.

Table 7.3 Determining caloric and macronutrient requirements (g/day): carbohydrates.

Total caloric requirement = [weight in kg] × 25 kcal/kg/day

½ × Total caloric requirements = carbohydrates calories ½ × Total caloric requirements = protein + lipid calories

Carbohydrates in grams = carbohydrate calories/calories per gram carbohydrate* = ½ × total caloric requirements/calories per gram carbohydrate = 0.5 × [weight in kg] × 25 kcal/3.4 kcal/g = [weight in kg] × 3.67 g/kg/day

^* Carbohydrates = 3.4 kcal/g; lipids = 10 kcal/g; protein = 4 kcal/g.

Table 7.4 Determining caloric and macronutrient requirements (g/day): lipids and proteins.

Lipid calories + protein calories = ½ × total caloric requirements

Protein calories = protein required (from Table 7.2) × calories per gram protein* = 1.5 g/kg/day × [weight in kg] (For critical illness) × 4 kcal/g

Lipids in grams = lipid calories/calories per gram lipid* = [(½ × total caloric requirements) – protein calories]/calories per gram lipid = [(½ × total caloric requirements) – protein calories]/10 kcal/g

^* Carbohydrates = 3.4 kcal/g; lipids = 10 kcal/g; protein = 4 kcal/g.