The parenteral nutrition formulation is a complex solution containing up to 40 different nutrients. The basic parenteral solution is composed of dextrose, amino acids, lipids, electrolytes, minerals, trace elements, vitamins, and water. Medications can also be added. Most commercial solutions contain the monohydrate form of dextrose that provides 3.4 kcal/g. Crystalline amino acids are used in parenteral nutrition formulations to provide protein and provide 4 kcal/g when oxidized. Lipid emulsions are available in 20% and 30% concentrations, which provide 2 kcal/mL and 3 kcal/mL respectively. The 30% concentration is approved only for compounding within a 3-in-1 admixture.
Parenteral nutrition administered via a central vein allows for administration of hyperosmolar solution (more than 1800 mOsm/L) and adequate nutrition delivery. The dextrose, amino acids, and electrolytes contribute to the osmotic load and can be given in higher concentrations as compared to peripheral parenteral nutrition. Lipid emulsions are isotonic and can be given via a central or peripheral vein.
Solutions with lower osmolarities (less than 900 mOsm/L) must be administrated via peripheral veins. Solutions for peripheral infusion usually contain 5–10% dextrose and 3% amino acids. These lower osmolarity solutions result in a high incidence of thrombophlebitis and line infiltration. These solutions may provide adequate protein for some patients, but inadequate total energy from dextrose, depending on volume limitations. Additional energy can be provided with lipid emulsions since these solutions are isotonic and well tolerated by peripheral veins.
Lipid emulsions can prevent EFAD and provide energy to patients on parenteral nutrition. There are four lipid emulsion products available for use in the United States. Two formulations are composed of long-chain triglycerides, derived from either 100% soybean oil, or 50% safflower oil and 50% soybean oil. The third formulation, Smoflipid, was created due to concerns about the high content of proinflammatory omega-6 polyunsaturated fatty acids in traditional lipid emulsions. Smoflipid is composed of 30% soybean oil, 30% medium-chain triglycerides, 25% olive oil, and 15% fish oil. The fourth emulsion, Clinolipid, is composed of 80% olive oil and 20% soybean oil. For all lipid emulsions, providers should follow manufacturer dosing recommendations to prevent complications associated with excessive fat administration or EFAD.
Parenteral nutrition solutions should be initiated at half of the estimated energy requirement, or approximately 100–150 g dextrose for the first 24 hours; they are increased daily as tolerated to prevent hyperglycemia and electrolyte abnormalities in patients at risk for refeeding syndrome. Amino acids and lipid emulsions can be started at target goals.
et al. Effect of supplemental parenteral nutrition versus enteral nutrition alone on clinical outcomes in critically ill adult patients: a systematic review and meta-analysis of randomized controlled trials. Nutrients. 2020;12:2968.
et al. American Society for Parenteral and Enteral Nutrition guidelines for the selection and care of central venous access devices for adult home parenteral nutrition administration. JPEN J Parenter Enteral Nutr. 2019;43:15.