Quantification of lung recruitment by respiratory mechanics and CT imaging: what are the clinical implications?

Acute respiratory distress syndrome (ARDS) is characterized by increased elastance of the lung and respiratory system (1). Depending on the precipitating factor, pulmonary vs. extrapulmonary, the distribution of pathologic findings and altered respiratory mechanics in the lung is heterogeneous (2). Portions of the lung can be collapsed and/or fluid-filled while others are well-aerated. In order to facilitate gas exchange, recruitment maneuvers are sometimes employed in patients with ARDS (3). These can be performed with a constant high pressure inspiratory hold for 30–40 seconds (4,5) or via stepwise recruitment by increasing the positive end-expiratory pressure (PEEP) (6), typically followed by application of PEEP at a higher level than the previous baseline to maintain aeration of the recruited lung units (7). Recruitment maneuvers have been proposed as useful tools in managing patients with ARDS in order to add previously non-participatory lung units to gas exchange as well as to assess disease severity. The potential effectiveness of recruitment maneuvers in incorporating previously collapsed lung units into gas exchange or in improving the distension of previously poorly aerated pulmonary units differs from patient to patient consequent to the variability in etiology of the lung injury and the heterogeneity of lung parenchyma (8).