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 cmHO, PEEP 15 cmHO).

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 cmHO and four end-inspiratory CT scans (from 19 to 40 cmHO). 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 cmHO 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 cmHO (i.e., always closed at plateau 30 cmHO) was 10 ± 29, 54 ± 86, 162 ± 92, and 185 ± 134 g 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 15 cmHO (63 ± 26 vs 39 ± 32 g in mild ARDS, p = 0.23; 92 ± 53 vs 78 ± 142 g 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 45 cmHO decreased the lung inhomogeneity slightly (but significantly) in mild and moderate ARDS, but not in severe ARDS.

Conclusions: Data show that the prerequisites of the open lung strategy are not satisfied using PEEP up to 15 cmHO and plateau pressure up to 30 cmHO. For an effective open lung strategy, higher pressures are required. Therefore, risks of atelectrauma must be weighted versus risks of volutrauma.

Trial Registration: Clinicaltrials.gov identifier: NCT01670747 ( www.clinicaltrials.gov ).