Opening pressures and atelectrauma in acute respiratory distress syndrome

Purpose Open lung strategy during ARDS aims to decrease the ventilator-induced lung injury by minimizing the atelectrauma and stress/strain maldistribution. We aim to assess how much of the lung is opened and kept open within the limits of mechanical ventilation considered safe (i.e., plateau pressure 30 cmH 2 O, PEEP 15 cmH 2 O). Methods Prospective study from two university hospitals. Thirty-three ARDS patients (5 mild, 10 moderate, 9 severe without extracorporeal support, ECMO, and 9 severe with it) underwent two low-dose end-expiratory CT scans at PEEP 5 and 15 cmH 2 O and four end-inspiratory CT scans (from 19 to 40 cmH 2 O). Recruitment was defined as the fraction of lung tissue which regained inflation. The atelectrauma was estimated as the difference between the intratidal tissue collapse at 5 and 15 cmH 2 O PEEP. Lung ventilation inhomogeneities were estimated as the ratio of inflation between neighboring lung units. Results The lung tissue which is opened between 30 and 45 cmH 2 O (i.e., always closed at plateau 30 cmH 2 O) was 10 ± 29, 54 ± 86, 162 ± 92, and 185 ± 134 g in mild, moderate, and severe ARDS without and with ECMO, respectively ( p