Abstract
BackgroundMultiple studies have identified single variables or composite scores that help risk stratify patients at the time of acute lung injury (ALI) diagnosis. However, few studies have addressed the important question of how changes in pulmonary physiologic variables might predict mortality in patients during the subacute or chronic phases of ALI. We studied pulmonary physiologic variables, including respiratory system compliance, P/F ratio and oxygenation index, in a cohort of patients with ALI who survived more than 6 days of mechanical ventilation to see if changes in these variables were predictive of death and whether they are informative about the pathophysiology of subacute ALI.MethodsNinety-three patients with ALI who were mechanically ventilated for more than 6 days were enrolled in this prospective cohort study. Patients were enrolled at two medical centers in the US, a county hospital and a large academic center. Bivariate analyses were used to identify pulmonary physiologic predictors of death during the first 6 days of mechanical ventilation. Predictors on day 1, day 6 and the changes between day 1 and day 6 were compared in a multivariate logistic regression model.ResultsThe overall mortality was 35%. In multivariate analysis, the PaO2/FiO2 (OR 2.09, p < 0.04) and respiratory system compliance (OR 3.61, p < 0.01) were predictive of death on the 6th day of acute lung injury. In addition, a decrease in respiratory system compliance between days 1 and days 6 (OR 2.14, p < 0.01) was independently associated with mortality.ConclusionsA low respiratory system compliance on day 6 or a decrease in the respiratory system compliance between the 1st and 6th day of mechanical ventilation were associated with increased mortality in multivariate analysis of this cohort of patients with ALI. We suggest that decreased respiratory system compliance may identify a subset of patients who have persistent pulmonary edema, atelectasis or the fibroproliferative sequelae of ALI and thus are less likely to survive their hospitalization.
Highlights
Multiple studies have identified single variables or composite scores that help risk stratify patients at the time of acute lung injury (ALI) diagnosis
Due to this high mortality, rescue therapies such as extracorporeal membrane oxygenation (ECMO), inhaled nitric oxide, prone positioning and high frequency oscillatory ventilation are often considered for patients who are perceived to be at the highest risk of death
In this prospective cohort study of 93 patients with ALI who survived 6 or more days of mechanical ventilation, we found that a low or decreasing respiratory system compliance on the 6th day of mechanical ventilation was associated with an increased risk of death
Summary
Multiple studies have identified single variables or composite scores that help risk stratify patients at the time of acute lung injury (ALI) diagnosis. Few studies have addressed the important question of how changes in pulmonary physiologic variables might predict mortality in patients during the subacute or chronic phases of ALI. We studied pulmonary physiologic variables, including respiratory system compliance, P/F ratio and oxygenation index, in a cohort of patients with ALI who survived more than 6 days of mechanical ventilation to see if changes in these variables were predictive of death and whether they are informative about the pathophysiology of subacute ALI. We performed a study of pulmonary physiologic variables in a cohort of patients who survived more than 6 days of mechanical ventilation. Through a physiologic investigation of pulmonary mechanics over the first 6 days of mechanical ventilation, we sought to develop a deeper understanding of the pulmonary pathophysiology that might lead to death during ALI
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