• Luciano Gattinoni, Federica Vagginelli, Davide Chiumello, Paolo Taccone, and Eleonora Carlesso.
• Istituto di Anestesia e Rianimazione, Universita' degli Studi di Milano, Ospedale Policlinico-IRCCS, Milano, Italy.
• Crit. Care Med. 2003 Apr 1;31(4 Suppl):S300-4.

ObjectivesTo review the physiologic approach to setting mechanical ventilation in acute lung injury/acute respiratory distress syndrome.Data SourcesMEDLINE search from 1979 to the present.Data SelectionPersonal selection of some articles we believe relevant for understanding acute lung injury/acute respiratory distress syndrome physiopathology and its physiologic management.Data SummaryKnowing the underlying pathology is key to estimating the potential for recruitment. The potential for recruitment is rather low when the consolidation of pulmonary units exceeds collapse, as in diffuse pneumonia. In contrast, when pulmonary unit collapse exceeds consolidation, as in acute lung injury/acute respiratory distress syndrome from extrapulmonary origin, the potential for recruitment may be high. To exploit the potential for recruitment, a transpulmonary pressure greater than the opening pressure must be applied to the lung. To do so, chest wall elastance must be measured or estimated. To avoid collapse after recruitment, a positive end-expiratory pressure greater than the compressive forces operating on the lung and an alveolar ventilation sufficient to prevent absorption atelectasis must be provided. Indeed, avoidance of stretch (low airway plateau pressure) and prevention of cyclic collapse and reopening (adequate positive end-expiratory pressure and alveolar ventilation) are the physiologic cornerstones of mechanical ventilation in acute lung injury/acute respiratory distress syndrome. When considering all the randomized clinical trials reported so far, it is tempting to speculate that transpulmonary pressure and stresses, rather than tidal volume per se, are the key factors that may have an impact on mortality.ConclusionsThe majority of physiologic, experimental, and clinical trial data converge on one simple concept: treat the lung gently.

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