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Methods

As part of a study on alveolar recruitment (https://clinicaltrials. gov, NCT02457741), we measured low-flow (5 L/min) inflation P–V curves at different PEEP levels in 30 patients who had moderate/severe ARDS due to different causes and were receiving deep sedation and neuromuscular blockers. All patients were ventilated in volume-controlled mode with a tidal volume of 6 ml/kg of predicted body weight. Both flow and pressure were measured with a differential pressure transducer and a pneumotachograph at the Y-piece. Flow and pressure were calibrated before measurements were obtained, and air leak was excluded through a 6-second end-inspiratory occlusion. The P–V curve (Figure 1) was started after a prolonged expiration (15–20 s) to minimize auto-PEEP. The low-flow technique was used to minimize the resistive component of airway pressure, thus allowing a very close estimate of the elastic …