Respiratory Mechanics, Lung Recruitability, and Gas Exchange in Pulmonary and Extrapulmonary Acute Respiratory Distress Syndrome

<jats:sec> <jats:title>Objectives:</jats:title> <jats:p>Acute respiratory distress syndrome is a clinical syndrome characterized by a refractory hypoxemia due to an inflammatory and high permeability pulmonary edema secondary to direct or indirect lung insult (pulmonary and extrapulmonary form). Aim of this study was to evaluate in a large database of acute respiratory distress syndrome patients, the pulmonary versus extrapulmonary form in terms of respiratory mechanics, lung recruitment, gas exchange, and positive end-expiratory pressure response.</jats:p> </jats:sec> <jats:sec> <jats:title>Design:</jats:title> <jats:p>A secondary analysis of previously published data.</jats:p> </jats:sec> <jats:sec> <jats:title>Patients:</jats:title> <jats:p>One-hundred eighty-one sedated and paralyzed acute respiratory distress syndrome patients (age 60 yr [46–72 yr], body mass index 25 kg/m<jats:sup>2</jats:sup> [22–28 kg/m<jats:sup>2</jats:sup>], and Pa<jats:sc>o</jats:sc> <jats:sub>2</jats:sub>/F<jats:sc>io</jats:sc> <jats:sub>2</jats:sub> 184 ± 66).</jats:p> </jats:sec> <jats:sec> <jats:title>Interventions:</jats:title> <jats:p>Lung CT scan performed at 5 and 45 cm H<jats:sub>2</jats:sub>O. Two levels of positive end-expiratory pressure (5 and 15 cm H<jats:sub>2</jats:sub>O) were randomly applied.</jats:p> </jats:sec> <jats:sec> <jats:title>Measurements and Main Results:</jats:title> <jats:p>Ninety-seven and 84 patients had a pulmonary and extrapulmonary acute respiratory distress syndrome. The median time from intensive care admission to the CT scan and respiratory mechanics analysis was 4 days (interquartile range, 2–6). At both positive end-expiratory pressure levels, pulmonary acute respiratory distress syndrome presented a significantly lower Pa<jats:sc>o</jats:sc> <jats:sub>2</jats:sub>/F<jats:sc>io</jats:sc> <jats:sub>2</jats:sub> and higher physiologic dead space compared with extrapulmonary acute respiratory distress syndrome. The lung and chest wall elastance were similar between groups. The intra-abdominal pressure was significantly higher in extrapulmonary compared with pulmonary acute respiratory distress syndrome (10 mm Hg [7–12 mm Hg] vs 7 mm Hg [5–8 mm Hg]). The lung weight and lung recruitability were significantly higher in pulmonary acute respiratory distress syndrome (1,534 <jats:italic toggle="yes">g</jats:italic> [1,286–1,835 <jats:italic toggle="yes">g</jats:italic>] vs 1,342 <jats:italic toggle="yes">g</jats:italic> [1,090–1,507 <jats:italic toggle="yes">g</jats:italic>] and 16% [9–25%] vs 9% [5–14%]).</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions:</jats:title> <jats:p>In the early stage, pulmonary acute respiratory distress syndrome is characterized by a greater impairment of gas exchange and higher lung recruitability. The recognition of the origin of acute respiratory distress syndrome is important for a more customized ventilatory management.</jats:p> </jats:sec>