• Maurizio Cereda, Kiarash Emami, Yi Xin, Stephen Kadlecek, Nicholas N Kuzma, Puttisarn Mongkolwisetwara, Harrilla Profka, Stephen Pickup, Masaru Ishii, Brian P Kavanagh, Clifford S Deutschman, and Rahim R Rizi.
• Department of Anesthesiology and Critical Care and Stavropoulos Sepsis Research Program, University of Pennsylvania, Philadelphia, PA, USA. maurizio.cereda@uphs.upenn.edu
• Crit. Care Med.. 2013 Feb 1;41(2):527-35.

ObjectiveAtelectasis and surfactant depletion may contribute to greater distension-and thereby injury-of aerated lung regions; recruitment of atelectatic lung may protect these regions by attenuating such overdistension. However, the effects of atelectasis (and recruitment) on aerated airspaces remain elusive. We tested the hypothesis that during mechanical ventilation, surfactant depletion increases the dimensions of aerated airspaces and that lung recruitment reverses these changes.DesignProspective imaging study in an animal model.SettingResearch imaging facility.SubjectsTwenty-seven healthy Sprague Dawley rats.InterventionsSurfactant depletion was obtained by saline lavage in anesthetized, ventilated rats. Alveolar recruitment was accomplished using positive end-expiratory pressure and exogenous surfactant administration.Measurements And Main ResultsAirspace dimensions were estimated by measuring the apparent diffusion coefficient of He, using diffusion-weighted hyperpolarized gas magnetic resonance imaging. Atelectasis was demonstrated using computerized tomography and by measuring oxygenation. Saline lavage increased atelectasis (increase in nonaerated tissue from 1.2% to 13.8% of imaged area, p < 0.001), and produced a concomitant increase in mean apparent diffusion coefficient (~33%, p < 0.001) vs. baseline; the heterogeneity of the computerized tomography signal and the variance of apparent diffusion coefficient were also increased. Application of positive end-expiratory pressure and surfactant reduced the mean apparent diffusion coefficient (~23%, p < 0.001), and its variance, in parallel to alveolar recruitment (i.e., less computerized tomography densities and heterogeneity, increased oxygenation).ConclusionsOverdistension of aerated lung occurs during atelectasis is detectable using clinically relevant magnetic resonance imaging technology, and could be a key factor in the generation of lung injury during mechanical ventilation. Lung recruitment by higher positive end-expiratory pressure and surfactant administration reduces airspace distension.

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