© 2008 American Thoracic Society
Enlarging and Protecting an Aerated LungTo the Editor:In their article, Dr. Terragni and colleagues show that tidal hyperinflation causes higher concentrations of inflammatory mediators and a lower number of ventilator-free days in a subpopulation of patients with 49% of nonaerated lung weight, in comparison with a subpopulation of patients with 26% of nonaerated lung weight (1). Consequently, they conclude that their results may confirm the notion that the best ventilatory strategy should be ideally adapted to the size of the aerated lung. Notwithstanding, these very important data clearly enable a different kind of approach in which the key issue is enlarging the aerated lung. Looking to protect the lungs of patients with acute respiratory distress syndrome from ventilator-induced lung injury (VILI), even when focused on significantly decreasing hyperinflation, we still must consider a maximum-recruitment strategy (2). This alternative concept is directed at maintaining an open lung (3) instead of passively adapting the ventilatory strategy to the size of the aerated lung. By obtaining massive recruitment, it is possible to decrease overdistension in the nondependent zones (2), likely due to an overall increase in pleural pressures. Under these circumstances, it is crucial that expiratory pressures are not allowed to fall below the closing pressures of most lung units. Thereby, we are also attenuating repeated derecruitment-associated lung injury (4). The new concept here is not to choose which mechanism of VILI is more critical to oppose, but rather to propose a strategy capable of minimizing both injury mechanisms simultaneously. Reinforcing the importance of minimizing tidal hyperinflation as demonstrated by Terragni and colleagues, and emphasizing the possible protective role of an adequate positive end-expiratory pressure (PEEP) after a massive recruitment, Tschumperlin and colleagues show that tidal stretch can be attenuated if the net deformation of the alveolar epithelial cell is minimal (5). Finally, we believe that the results of the study by Terragni and colleagues bring up the important question of the value of permissive atelectasis. Strategies trying to overcome a false tradeoff between privileging overdistension or repeated derecruitment must be considered and clinically evaluated before accepting a closed lung.
Universidade de São Paulo FOOTNOTES Conflict of Interest Statement: J.B.B. has no financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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