Abstract
The rate, amount, and type of lipids provided intravenously are important aspects regarding the efficacy and safety in neonates and children. Intravenous lipid emulsions (ILEs) are an indispensable part of paediatric parenteral nutrition (PN) as a non-carbohydrate source of energy delivered as an iso-osmolar solution in a low volume (2.0 kcal/mL with 20% ILEs, or 1.1 kcal/mL with 10% ILEs due to the higher relative content of glycerol).
Generally a lipid intake of 25-50% of non-protein calories is recommended in fully parenterally fed patients (see also section on "Energy" of these guidelines). Lipids provide essential fatty acids (EFAs) and help with the delivery of the lipid soluble vitamins A, D, E, and K.
The ILE particle is metabolized following the same pathway as a natural chylomicron. The triglyceride portion is hydrolysed by the endothelial lipoprotein lipase (LPL).
In the circulation, ILE particles also exchange apoproteins and cholesterol with endogenous lipoproteins, thus transforming the initial ILE particle into a so-called remnant particle. The liver rapidly removes ILE remnant particles by hydrolysing them with hepatic lipase.
The released free fatty acids (FFAs) can be captured by the adjacent tissues or can circulate bound to albumin, for use in other tissues or uptake by the liver. The rate of hydrolysis varies according to the type of the triglyceride substrate (i.e., length of the FA, degree of saturation, position of the FA on the glycerol).
LPL activity is influenced by prematurity, malnutrition, hypoalbuminaemia, metabolic acidosis, high plasma lipid concentrations, and may be reduced in catabolic states. If the ILE is infused at a rate that exceeds the rate of utilisation, plasma triglyceride concentration will rise and may cause adverse effects including reticulo-endothelial system overload.
If the rate of hydrolysis exceeds the rate at which the released FFAs are taken up and oxidized, the plasma concentration of FFAs will also increase and in turn may decrease the LPL activity.