The body responds to a diverse range of insults, such as surgery, infection and injury by the activation of a wide range of cell types of the immune system, creating a number of potent cellular actions and mediators. The inflammatory response, although essential for fighting infection, may damage the host. Its strength depends on pro- and anti-inflammatory mediators, cytokines and lipid mediators being the key mediators.
Recently, Robert Grimble, from the Institute of Human Nutrition, School of Medicine, University of Southampton, UK has reviewed the fatty acid profile of modern lipid emulsions, and the scientific considerations for creating the ideal composition.
In his report published in volume 1 of Clinical Nutrition Supplements, he states that in some types of patients, the lack of a correctly functioning gut precludes complete oral or enteral nutrient provision. As a consequence, the intravenous route assumes a greater importance for the provision of energy substrates, amino acids and micronutrients. Reliance on glucose as the main provider of energy to patients requiring intravenous nutrition led to metabolic complications. These include insulin insensitivity and metabolic acidosis due to the need to dispose of a large amount of metabolic breakdown products in the form of carbon dioxide.
Intravenous nutrition has been a life-saving technique in the treatment of severely ill patients, particularly in those where normal gut function is absent. However, the inability to provide sufficient energy to patients, in the form of glucose, led to the development of intravenous lipid emulsions.
These products were a major breakthrough in clinical nutrition particularly as insulin insensitivity is a major feature in the metabolism of severely ill patients.
Previous studies have indicated that the use of lipid emulsions in clinical nutrition is not without limitations, but the inclusion of ¨-3 fatty acids and fats rich in MUFAs and anti-oxidants in intravenous nutrition may successfully modulate inflammation and immunosuppression.
The creation of soybean oil-based lipid emulsions, for use in parenteral nutrition, was an important landmark in the science of nutritional treatment of surgical patients and individuals requiring critical care.
The primary importance of this development was that the energy requirements of the patient could be met without the metabolic burden imposed by high-level glucose infusion in situations of respiratory distress and insulin insensitivity. In soybean oil-based emulsions the ratio of ¨-6 to ¨-3 fatty acids is approximately 7:1. These classes of fatty acids compete for inclusion in cell membranes and result in the production of lipid mediators of differing potency.
The authors concludes on the note that recent studies suggest that increasing the ratio of ¨-3 to ¨-6 fatty acids and raising the monounsaturated fatty acid (MUFA) content of intravenous lipid emulsion is beneficial. MUFAs exert a neutral effect on metabolism. Thus ideal lipid solutions can be designed by adjustment of the ratio of ¨-3, ¨-6 and MUFAs.