The influence of a PEEP-wave maneuver on lung recruitment in healthy and injured lungs: a study in mechanically ventilated pigs

Complete alveolar recruitment is the main goal of lung-protective ventilation strategy which is reached either (i) by intermittent recruitment maneuvers or (ii) by titration of the end-expiratory pressure (PEEP) on the basis of the analysis of the patient individual lung mechanics. We investigated the relationship between PEEP and alveolar recruitability both in healthy and injured lungs in mechanically ventilated pigs (n=20). The animals were allocated in random order to lung-healthy control group (n=10) or to the lung-injury group (n=10). Acute lung injury was induced by systemic application of oleic acid. All animals were mechanically ventilated in the pressure-controlled mode (PCV) and undergoing two PEEP-wave maneuvers during the entire intervention. The volume-dependent intratidal compliance was calculated using the gliding-SLICE method. The alveolar recruitability was analyzed by the comparison of the volume-dependent intratidal compliance at the identical PEEP-levels which were realized two times per maneuver, during the increasing and during the decreasing PEEP-sequence of the PEEP-wave maneuver. We found in 97% of all lung-injured animals an increase of the compliance by the decremental PEEP trial with respect to the incremental one. Hence, the recruitability in lung-injured animals is significantly larger than in lung-healthy animals. We conclude that alveolar recruitability is higher in acute lung injury and one should pay attention on the recruitment state in the clinical setting of acute lung injury. From the methodical point of view we conclude that our method of compliance difference analysis between the situation preceding and following a recruitment maneuver allows non-invasive analysis of alveolar recruitability.