Short-term lung metabolic effects of middle-chain triglyceride/long-chain triglyceride-containing lipid emulsions in patients with post-traumatic acute respiratory distress syndrome

Enhanced lipid peroxidation is a contributing factor for oxidative stress in patients with acute respiratory distress syndrome (ARDS). middle-chain triglyceride (MCT)/long-chain triglyceride (LCT)-containing fat emulsions have lower polyunsaturated fatty acid content, higher concentrations of antioxidants (alpha-tocopherol) and reduced susceptibility to peroxidation reactions compared with LCT-containing fat emulsions, which possess strong proinflammatory and oxidative damage potential [1]. The aim of this study was to compare pulmonary metabolic effects of these two fat emulsions. We prospectively measured intrapulmonary oxygen consumption (VO₂ipulm), lung lactate production (LLP), glucose flux trough the lung (GF), energy expenditure (EE) and respiratory quotient (RQ) in 26 adult post-traumatic ARDS patients, receiving conventional fat emulsion. At study entry patients were randomly switched from LCT to MCT/LCT lipid emulsion. The patients in the LCT group (n = 13) continued to receive conventional 20% LCT-containing fat emulsion, and in the MCT/LCT group (n = 13) a 20% MCT-containing fat emulsion was started. In both groups fat emulsion was infused in doses of 1 g/kg/day. VO₂ipulm was estimated by subtracting the calculated VO₂ using the reverse Fick method from the whole body VO₂ using indirect calorimetry (Datex Ohmeda M-COVX metabolic monitor). All measurements and calculations were performed simultaneously after achieving steady-state conditions in 2-hour periods for 24 hours. The overall mortality in this setting was 64%. We found substantial increases in VO₂ipulm as a component of the whole body VO₂ in both groups (median 29.3%; interquartile range 26.2–34.1%). In the MCT/LCT group there was an abrupt (mean value 26 ± 11 min) and sustained significant increase in EE (mean 3.4 ± 0.3 kcal/kg) with a maximal corresponding increase in whole body VO₂ on the 6th hour. VO₂ipulm showed a constant decline, reaching minimum median values of 20.4% (interquartile range 17.1–22.4%) of the whole body VO₂ on the 8th hour. The absolute value of VO₂ipulm also decreased from 2.1 ± 0.4 ml/kg/min to 1.3 ± 3 ml/kg/min. These changes not accompanied by significant variations in LLP, GF and RQ. We concluded that the observed decrease in VO₂ipulm in the MCT/LCT group with concomitant increases in whole body VO₂ and EE without any significant changes in RQ, LLP and GF is indicative for increased oxygen consumption for metabolic purposes outside the lung. These data suggest that infusion of a MCT-containing fat emulsion could lead to a significant decrease of oxygen used by the lung for nonmetabolic purposes (i.e. free radical formation from lipid peroxidation). The observed positive short-term metabolic effects of MCT/LCT-containing fat emulsions could have potential clinical applications in reducing oxidative damage, caused by a large inflammatory mass of the lung in ARDS patients.