Early time-course of respiratory mechanics, mechanical power and gas exchange in ARDS patients

Purpose: To describe the clinical course of ARDS during the first three days of mechanical ventilation, to compare ventilatory setting, respiratory mechanics and gas exchange variables collected during the first three days of mechanical ventilation between patients who survived and died during intensive care unit (ICU) stay and to investigate the variables associated with mortality at ICU admission and throughout the first three days of mechanical ventilation. Materials and methods: Prospective observational study. Mechanically ventilated ARDS patients were studied at ICU admission and for the following three days. Univariate logistic regression models were performed for PaO2/ FiO2 ratio, driving pressure and alveolar dead space fraction and for mechanical power and mechanical power ratio.Results: Mechanical power ratio was higher in non survivors at ICU admission and over time; PaO2/FiO2 ratio was higher in survivors with a similar behavior over time in the two groups while alveolar dead space fraction was similar at ICU admission and over time between groups. Mechanical power ratio was the only physiological variable which remained consistently associated with ICU mortality throughout the study.Conclusions: The alteration in oxygenation, dead space, and mechanical power ratio should be assessed not at intensive care admission, but during the first days of mechanical ventilation to better predict outcome.