Inhomogeneity of lung parenchyma during the open lung strategy: a computed tomography scan study

Inhomogeneity of Lung Parenchyma during the Open Lung Strategy A Computed Tomography Scan Study Salvatore Grasso1, Tania Stripoli1, Marianna Sacchi1, Paolo Trerotoli2, Francesco Staffieri3, Delia Franchini3, Valentina De Monte3, Valerio Valentini3, Paolo Pugliese4, Antonio Crovace3, Bernd Driessen5,6, and Tommaso Fiore1 1Dipartimento dell’Emergenza e Trapianti d’Organo (DETO), Sezione di Anestesiologia e Rianimazione, 2Dipartimento di Scienze Biomediche ed Oncologia Umana, Cattedra di Statistica Medica, 3Dipartimento dell’Emergenza e Trapianti d’Organo (DETO), Sezione di Chirurgia Veterinaria, and 4Dottorato in Scienze Chirurgiche Sperimentali e Terapie Cellulari, Universita` degli Studi di Bari, Bari, Italy; 5Department of Clinical Studies-NBC, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, Pennsylvania; and 6Department of Anesthesiology, David Geffen School of Medicine at UCLA, Los Angeles, California Rationale : Theopen lung strategy aims at reopening (recruitment) of nonaerated lung areas in patients with acute respiratory distress syndrome, avoiding tidal alveolar hyperinflation in the limited area of normally aerated tissue (baby lung). Objectives:We tested the hypothesis that recruited lung areas do not resume elastic properties of adjacent baby lung. Methods: Twenty-five anesthetized, mechanically ventilated pigs were studied. Four lung-healthy pigs served as controls and the remaining 21 were divided into three groups (n 5 7 each) in which lung injury was produced by surfactant lavage, lipopolysaccharide infusion, or hydrochloride inhalation. Computed tomography scans, respiratory mechanics, and gas exchange parameters were recorded under three conditions: at baseline, during lung recruitment maneuver, and at end-expiration and end-inspiration when ventilating after an open lung protocol. Measurements and Main Results: During recruitment maneuver and openlungprotocol, thegas volumeenteringthe insufficiently aerated compartment was 96% (75–117%) and 48% (41–63%) (median [interquartile range]) of the functional residual capacity measured before and at zero end-expiratory pressure, respectively. Nonetheless, the volume of hyperinflated lung increased during both recruitment maneuver (by 1–28% of total lung volume; P , 0.01) and open lung protocol ventilation at end-inspiration (by 1–15% of total lung volume; P , 0.01). Regional elastance of recruited lung tissue was consistently higher than that of the baby lung regardless of the ARDS model (P , 0.01). Conclusions: Alveolar recruitment is not protective against hyperinflation of thebabylung because lung parenchymaisinhomogeneous during ventilation with the open lung strategy.