Lung opening and closing during ventilation of acute respiratory distress syndrome

Rationale: The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which varies widely during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, that is, alveolar strain and intratidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter). Objectives: To investigate how lung recruitability influences alveolar strainandintratidalopeningandclosing after the application of high PEEP. Methods:We analyzed data from a database of 68 patients with acute lung injury or ARDS who underwent whole-lung computed tomography at 5, 15, and 45 cm H2O airway pressure. Measurements and Main Results: End-inspiratory nonaerated lung tissue was estimated from computed tomography pressure–volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cm H2O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase in PEEPmarkedly reduced opening and closing lung tissue (P , 0.001), whereas no differences were observed in patients with a lower percentage of potentially recruitable lung. In contrast, alveolar strain similarly increased in the two groups (P 5 0.89). Opening and closing lung tissuewasdistributedmainly in the dependent andhilar lung regions, andit appearedtobe an independent risk factor fordeath (odds ratio, 1.10 for each 10-g increase). Conclusions: In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intratidal alveolar opening and closing by increasing PEEP prevails over the effects of increasing alveolar strain.