The use of intravenous lipids is essential to a complete TPN regimen. Lipids serve as a source of linoleic acid to prevent or treat essential fatty acid deficiency (EFAD), and as an energy source. Larger quantities serve as a partial replacement for glucose as a major source of calories (balanced TPN).
The VLBW infant is especially susceptible to the development of EFAD because tissue stores of linoleic acid are small and requirements for essential fatty acids are large secondary to rapid growth. The human fetus depends entirely on placental transfer of essential fatty acids. A VLBW infant with limited nonprotein energy reserve must mobilize fatty acids for energy when receiving intravenous nutrition devoid of lipid. Our own studies in these infants confirm other studies that show that biochemical evidence of EFAD can develop in the VLBW infant during the first week of life on lipid-free regimens.
Standard 20% emulsions contain a lower phospholipids emulsifier/triglycerides ratio than standard 10% lipid emulsions and should preferably be used for TPN. Clearance of lipid emulsions from the blood depends on the activity of lipoprotein lipase. Post-heparin lipoprotein lipase activity can be increased by relatively high doses of heparin; heparin does not improve utilization of intravenous lipids. Therefore the increase in lipase activity by heparin lends to an increase in FFAs which may exceed the infants ability to clear the products of lipolysis. The premature infant can clear 0.15 to 0.2 g/kg/hr of lipids.