ARDSNet. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000;342:1301-8.
Question: There is evidence that “stretch” in the lungs caused by high pressure can damage lung epithelium and increase inflammation. In ventilated patients who develop ARDS or acute lung injury, will reducing tidal volumes–which had been avoided because of worry of respiratory acidosis–improve their clinical outcome?
861 patients with acute lung injury and acute respiratory distress syndrome were randomly assigned to a conventional tidal volume arm (beginning with 12 ml per kilogram of predicted body weight to reach a plateau pressure 50 mm H2O) or a low tidal volume arm (beginning with 6 ml per kilogram of predicted body weight to reach a plateau pressure 30 mm H2O).
The trial was actually stopped early because significant benefits were found for the low-volume group. Mortality was 22% lower in the low-volume group (31.0%) compared to the conventional tidal volume group (39.8%, p=0.007). Circulatory failure, renal failure, and coagulation failure rates were also lower in the low-volume group. The low-volume group also had more ventilator-free days.
It should be pointed out that ventilation is a dynamic process and there were other variables that the authors adjusted that helped the low-volume group. The low-volume group required a slightly higher PEEP setting (around 9 as opposed to 8 cm H2O). The low-volume group was also allowed to get bicarbonate for correction of acidosis. Furthermore, the low-volume group did have a very slightly lower arterial oxygenation level compared to the traditional-volume group–but it doesn’t appear to have been clinically significant.
Interestingly, barotrauma rates remained the same, which the authors pointed out seemed to be independent of airway pressures.
Bottom line: While every patient’s clinical scenario is going to be different, because of this paper, most patients on mechanical ventilation are started at a tidal volume of 6-8 ml/kg.