Background In ARDS patients, changes in respiratory mechanical properties and ventilatory settings can cause incomplete lung deflation at end-expiration. Both can promote dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEP). The aim of this study was to investigate, in a large population of ARDS patients, the presence of intrinsic PEEP, possible associated factors (patients' characteristics and ventilator settings), and the effects of two different external PEEP levels on the intrinsic PEEP. Methods We made a secondary analysis of published data. Patients were ventilated with a tidal volume of 6-8 mL/kg of predicted body weight, sedated, and paralyzed. After a recruitment maneuver, a PEEP trial was run at 5 and 15 cmH.sub.2O, and partitioned mechanics measurements were collected after 20 min of stabilization. Lung computed tomography scans were taken at 5 and 45 cmH.sub.2O. Patients were classified into two groups according to whether or not they had intrinsic PEEP at the end of an expiratory pause. Results We enrolled 217 sedated, paralyzed patients: 87 (40%) had intrinsic PEEP with a median of 1.1 [1.0-2.3] cmH.sub.2O at 5 cmH.sub.2O of PEEP. The intrinsic PEEP significantly decreased with higher PEEP (1.1 [1.0-2.3] vs 0.6 [0.0-1.0] cmH.sub.2O; p Conclusions In sedated, paralyzed ARDS patients without a known obstructive disease, the amount of intrinsic PEEP during lung-protective ventilation is negligible and does not influence respiratory mechanical properties. Keywords: Acute respiratory distress syndrome, Intrinsic positive end-expiratory pressure, Respiratory mechanics, Gas exchange
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