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Ventilator-induced lung injury (VILI) may occur with both lung volumes that lead to overdistention of lung units (volutrauma) or with low distending pressures that allow the lung to be recruited and derecruited (atelectrauma).
VILI may cause injury in previously healthy regions of lung, and may also lead to multiorgan dysfunction.
To reduce the risk of VILI, limitation of end-inspiratory stretch using low tidal volumes ∼6 mL/kg and limiting plateau pressure (Pplat) <30 cm H2O should be used in treating most patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Higher Pplat may be used in patients with poorly compliant chest walls.
The appropriate level of positive end-expiratory pressure remains to be determined, but levels of PEEP that minimize atelectasis may be beneficial.
Permissive hypoventilation (hypercapnia) may be a necessary component of a lung-protective ventilator strategy.
The penetrance of lung-protective ventilation strategies into clinical practice is improving.
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There is consistent and convincing evidence that mechanical ventilation, particularly in the setting of lung injury, can contribute to functional and structural alterations in the lung. The experimental evidence has also led to the notion that mechanical ventilation not only perpetuates lung injury, but also contributes to both the morbidity and mortality of the acute respiratory distress syndrome (ARDS). Concern surrounding ventilator-induced lung injury (VILI) culminated in a consensus conference in 1993 that recommended (based solely on studies in animal models of ARDS) tidal volumes be limited to the range of 5 to 7 mL/kg and plateau pressures less than 35 cm H2O.1 It would be 8 years until the recommendations of the consensus group were affirmed by a randomized controlled trial demonstrating that a lung-protective strategy led to a decrease in mortality in patients with acute lung injury.2 After initial hesitations about the incorporation of these concepts into widespread clinical practice,3 lower tidal volumes and higher levels of positive end-expiratory pressure (PEEP) are being used widely to minimize VILI.4,5
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The objectives of this chapter are to review current concepts of VILI and provide the rationale for lung-protective ventilation strategies. Since most studies evaluating VILI have focused on ARDS, the relevant features of ARDS as it pertains to VILI will be reviewed first. Then, the concept of lung-protective ventilation strategies will be discussed, and pertinent studies evaluating these newer strategies in patients with ARDS will be presented. Recommendations based on current clinical evidence, and when this is lacking best experimental evidence, will also be presented (Table 51-1).
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