Short-term lung metabolic effects of middle-chain triglyceride/long-chain triglyceride-containing lipid emulsions in patients with post-traumatic acute respiratory distress syndrome
© BioMed Central Ltd. 2004
Published: 15 March 2004
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 . 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.