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- Ventilator-induced lung injury may occur with both lung volumes that lead to overdistention of lung units (volutrauma) or with low distending pressures that lead to the development of atelectasis (atelectrauma).
- Ventilator-induced lung injury may cause injury in previously healthy regions of lung, and may also lead to multiorgan dysfunction.
- To reduce the risk of ventilator-induced lung injury, low tidal volumes of 6 mL/kg should be used in treating most patients with acute respiratory distress syndrome.
- The appropriate level of positive end-expiratory pressure remains to be determined, but levels of PEEP that minimize atelectrauma may be beneficial.
- Permissive hypoventilation (hypercapnia) may be a necessary component of a lung-protective ventilatory strategy.
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There is consistent and convincing experimental 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 led to the notion that mechanical ventilation not only perpetuates the 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 made (based solely on studies in animal models of ARDS) the empirical recommendation to limit tidal volumes 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 designed to limit VILI would lead to an improvement in patient outcome.2 Unfortunately, it seems that it may take even longer until there is incorporation of these concepts into widespread clinical practice.3
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The objectives of this chapter are to develop the concept of VILI and provide the rationale for the shift in ventilation philosophy for patients with ARDS. First, the relevant features of ARDS as it pertains to VILI will be reviewed, since most of the studies evaluating VILI have focused on ARDS. 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 37-1).
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