Clinical Trials Using Conventional Mechanical Ventilation

Five different randomized trials were conducted in the 1990s to test modified mechanical ventilation strategies in ARDS patients (Table 1). One of these trials compared clinical outcomes in ARDS patients randomized to receive either a conventional approach with generous Vt and relatively low levels of PEEP to those randomized to receive small Vt and relatively high levels of PEEP [31]. Patients in the small VT/higher PEEP group also received recruitment maneuvers (continuous positive pressure airway pressure [CPAP] of 40 cmH2O for 40 seconds) to reverse atelectasis. Oxygenation was substantially improved with the small VT/high PEEP approach. Thus, higher levels of PEEP can compensate for the deleterious effects of the small Vt approach on oxygenation. The small VT/higher PEEP approach was also associated with respiratory acidosis, as expected. However, the small VT/higher PEEP approach was associated with substantially improved survival. These striking results demonstrated that the approach to mechanical ventilation could alter clinical outcomes and suggested that mechanical ventilation approaches should be modified from those that were used in the past. However, it was not clear if the improved outcomes were attributable to the use of smaller VT, higher PEEP, recruitment maneuvers, or the possibility of some unrecognized imbalances between the study groups [32]. Moreover, because this was a relatively small trial that involved many patients with causes of ARDS that are uncommon in other intensive care environments, it was important to confirm the findings.

Table 1. Clinical trials of lung-protective mechanical ventilation strategies in patients with ARDS. Values shown for tidal volumes are as reported in the studies.

Study

Tidal volumes (ml/kg)

Higher

Lower

Higher

Lower

Amato et al.[31] a

~12

~6

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