Relationship between intrapulmonary oxygen consumption and oxygenation index in patients with post-traumatic acute respiratory distress syndrome
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KeywordsAcute Respiratory Distress Syndrome Obstructive Lung Disease Oxygenation Index Indirect Calorimetry Acute Respiratory Distress Syndrome Patient
Post-traumatic acute respiratory distress syndrome (ARDS) is a stereotyped response caused by a variety of pulmonary and extrapulmonary insults following major trauma. Increased intrapulmonary oxygen consumption (VO2ipulm) was described in different conditions with impairment of lung function, including septic patients with ARDS  and patients with pneumonia . In this study we measured intrapulmonary oxygen consumption and oxygenation index (OI = Paw × FiO2 × 100/PaO2) in order to describe and compare the time course of these variables on the 1st, 3rd, 7th, 10th and 14th day after the ARDS onset. The study was performed in our level 1 trauma center ICU. We prospectively measured all hemodynamic and oxygen transport variables, including VO2ipulm and OI in 37 adult ventilated trauma patients, who fulfil the ARDS criteria according to the North American Concensus Conference. All patient were post-traumatic, ventilated with volume-controlled mode, and were included in the study if they met the above criteria at any time during their ICU stay. We excluded those patients with history of Chronic Obstructive Lung Disease and those ventilated with FiO2 > 0.80. VO2ipulm was estimated by subtracting calculated VO2 using the reverse Fick method from whole body VO2using indirect calorimetry (Datex Ohmeda M-COVX metabolic monitor). All measurements and calculations were performed simultaneously during steady-state conditions four times daily and the mean values were taken. The overall mortality in this setting was 57%. We found substantial increases in VO2ipulm as a component of whole body VO2 in all patients with post-traumatic ARDS (median 31.3%; interquartile range 27.2–34.1%) and good positive correlation between VO2ipulm and OI on the 3rd, 7th, 10th and 14th day, but not on the first day after the onset of ARDS. Our data suggest that VO2ipulm can be used as an additional pulmonary injury severity parameter but large observational studies are needed to link this variable with mortality in post-traumatic ARDS patients.