Opening pressures and atelectrauma in acute respiratory distress syndrome

Abstract

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 30cmH2O, PEEP 15cmH2O). 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 15cmH2O and four end-inspiratory CT scans (from 19 to 40cmH2O). 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 15cmH2O PEEP. Lung ventilation inhomogeneities were estimated as the ratio of inflation between neighboring lung units. The lung tissue which is opened between 30 and 45cmH2O (i.e., always closed at plateau 30cmH2O) was 10±29, 54±86, 162±92, and 185±134g in mild, moderate, and severe ARDS without and with ECMO, respectively (p<0.05 mild versus severe without or with ECMO). The intratidal collapses were similar at PEEP 5 and 15cmH2O (63±26 vs 39±32g in mild ARDS, p=0.23; 92±53 vs 78±142g in moderate ARDS, p=0.76; 110±91 vs 89±93, p=0.57 in severe ARDS without ECMO; 135±100 vs 104±80, p=0.32 in severe ARDS with ECMO). Increasing the applied airway pressure up to 45cmH2O decreased the lung inhomogeneity slightly (but significantly) in mild and moderate ARDS, but not in severe ARDS. Data show that the prerequisites of the open lung strategy are not satisfied using PEEP up to 15cmH2O and plateau pressure up to 30cmH2O. For an effective open lung strategy, higher pressures are required. Therefore, risks of atelectrauma must be weighted versus risks of volutrauma. Clinicaltrials.gov identifier: NCT01670747 ( www.clinicaltrials.gov ).