Opening pressures and atelectrauma in acute respiratory distress syndrome

Abstract

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

Does high PEEP prevent alveolar cycling?

“…4) and this pattern was similar independently of ARDS severity [18]. The absolute and percentage amount of collapse and decollapse increased with ARDS severity, but the effect of PEEP was similar in the three groups [18].…”

“…When a tidal volume/plateau pressure are applied, they overcome the surface forces at the level of the small airways and open up the previously collapsed lung units [18]. .…”

“…1 shows the effect of different tidal volumes, and consequently opening pressures on a collapsed ARDS lung ventilated at zero end-expiratory pressure (ZEEP). The amount of collapsed lung tissue that regains inflation depends on the plateau pressure/ tidal volume applied, and the greater the applied plateau pressure, the greater the amount of lung tissue undergoing intratidal collapse and decollapse [18].…”

“…Direct proof of VILI is nearly impossible to obtain in "real" ARDS patients, but a recent PET study [16] showed that the nonhomogeneous lung regions at the interface between collapsed and inflated lung tissue, where putatively intra-tidal collapse and decollapse occur, are always inflamed. Despite the relevance of the issue of opening and closing, just two studies measured intra-tidal collapse and decollapse at two different PEEP levels keeping the tidal volume constant and both were unable to demonstrate a significant intra-tidal collapse and decollapse reduction [11,18]. We measured intra-tidal collapse and decollapse in 34 ARDS patients (18 severe ARDS) keeping the tidal volume constant at two PEEP levels, 5 and 15, which are close to the PEEP levels applied in all clinical trials.…”

“…Upon recruitment, especially in the more severe patients, one may see an increase in poorly inflated tissue, [10], which is strongly related to the lung inhomogeneity [15]. The lung inhomogeneity itself is not completely abolished, but is slightly reduced or may paradoxically increase [18].…”