Components of Parenteral Nutrition

Introduction

• Macronutrients (ie, water, protein, dextrose, and IV fat emulsion [IVFE]) are used for energy (dextrose, fat) and as structural substrates (protein and fats).
• Protein is provided as crystalline amino acids (CAAs). When oxidized, 1 g of protein yields 4 calories (~17 J). Including the caloric contribution from protein in calorie calculations is controversial; therefore, PN calories can be calculated as either total or nonprotein calories.
• Standard CAA products contain a balanced profile of essential, semiessential, and nonessential L-amino acids and are designed for patients with “normal” organ function and nutritional requirements. Standard CAA products differ in amino acid, total nitrogen, and electrolyte content but have similar effects on protein markers.
• The primary energy source in PN solutions is carbohydrate, usually as dextrose monohydrate which is available in concentrations ranging from 5% to 70%. When oxidized, 1 g of hydrated dextrose provides 3.4 kcal (14.2 kJ).
• Commercially available intravenous fat emulsions (IVFEs) provide calories and essential fatty acids.

These products differ in triglyceride source, fatty acid content, and essential fatty acid concentration.

• When oxidized, 1 g of fat yields 9 kcal (38 kJ). Because of the caloric contribution from egg phospholipid and glycerol, caloric content of IVFE is 1.1 kcal/mL (4.6 kJ/ mL) for the 10%, 2 kcal/mL (8.4 kJ/mL) for the 20%, and 3 kcal/mL (12.6 kJ/mL) for the 30% emulsions.
• Essential fatty acid deficiency can be prevented by giving IVFE, 0.5 to 1 g/kg/day for neonates and infants and 100 g/wk for adults.
• IVFE 10% and 20% products can be administered by a central or peripheral vein, added directly to PN solution as a total nutrient admixture (TNA) or three-in-one system (lipids, protein, glucose, and additives), or piggybacked with a CAA and dextrose solution, commonly referred to as a two-in-one solution. IVFE 30% is approved only for TNA preparation.
• Micronutrients (ie, vitamins, trace elements, and electrolytes) are required to support metabolic activities for cellular homeostasis such as enzyme reactions, fluid balance, and regulation of electrophysiologic processes.
• Multivitamin products have been formulated to comply with guidelines for adults, children, and infants.

These products contain 13 essential vitamins, including vitamin K.

• Requirements for trace elements depend on the patient’s age and clinical condition. Examples include using higher doses of zinc in patients with high-output ostomies or diarrhea; restricting or withholding manganese and copper in patients with cholestatic liver disease; and restricting or withholding chromium, molybdenum, and selenium in patients with renal failure.
• Chromium, copper, manganese, selenium, and zinc are considered essential and available as single- or multiple-entity products for addition to PN solutions.
• Sodium, potassium, calcium, magnesium, phosphorus, chloride, and acetate are necessary components of PN for maintenance of numerous cellular functions.
• Electrolyte requirements depend on the patient’s age, disease state, organ function, drug therapy, nutrition status, and extrarenal losses.