To avoid these side effects the second generation lipid emulsions were developed. These contain a combination of medium- and long-chain fatty acids (MCT/LCT) with lower w-6 fatty acid content. MCT/LCT lipid emulsions are safe and do not produce biochemical or metabolic alterations or gaseous exchange in patients with ARDS. MCT/LCT combinations seem to reduce the generation of eicosanoids and do not alter the immune response in in-vitro and experimental studies. The impact of these differences on the nosocomial infection and the clinical prognosis of the patients has not been studied sufficiently despite the fact that some studies show reduced mortality and morbidity using MCT/LCT emulsions when compared with the use of pure LCT emulsions. MCT/LCT emulsions are normally used in clinical practice on patients that have required parenteral nutrition for 20 years.