Long-term effects of two protective-ventilation strategies in an ARDS model: Open Lung Approach by EIT versus ARDSnet
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KeywordsAcute Respiratory Distress Syndrome Electric Impedance Tomography Impedance Tomography Recruitment Maneuver Lung Collapse
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Different ventilatory strategies for the acute respiratory distress syndrome have been proposed. The Open Lung Approach (OLA) emphasizes the recruitment of airway units with avoidance of tidal recruitment. The ARDSnet strategy simply emphasizes the reduction of and hyperdistension. We studied the long-term VT consequences of both strategies in a controlled experiment where pigs where randomized and submitted to one of both strategies for 48 hours. Lung injury was induced by saline lavage followed by 3 hours of injurious mechanical ventilation. In the OLA arm, PEEP was selected by the EIT after a recruitment maneuver (RM), trying to keep lung collapse to a minimum, while the ARDSnet group followed a PEEP × FiO2 table. We scrutinized lung function at the end of a 48-hour period of lung protection, after a standardized RM. The concept was to provide equivalent conditions for lungs to perform, irrespective of lung history or treatment in previous days, in terms of gas exchange or alveolar stability during slow-deflation maneuvers. Before sacrifice and after maximum RM, we collected blood gases and expiratory pressure versus ΔZ (impedance changes by electric impedance tomography). Oxygenation and alveolar stability were equally impaired in both arms after injury. However, at the end of the 48 hours there was significant improvement in the capacity of oxygenation in the OLA arm (mean = 494 mmHg; P = 0.043), but not in the ARDSNet arm (mean = 278; P = 0.285). The potential to maintain airspace volumes improved along the protective period in the OLA arm, but deteriorated in the ARDSnet arm. (See Figure 1.)
Even after full reversal of atelectasias, lung function seems to be severely impaired after 48 hours of the ARDSnet strategy, as compared with OLA.
© BioMed Central Ltd 2009