Pulmonary mechanics and mortality in mechanically ventilated patients without acute respiratory distress syndrome: A cohort study

Background: Driving pressure has been proposed as a major determinant of outcome in patients with acute respiratory distress syndrome (ARDS), but there is little data examining the association between pulmonary mechanics, including driving pressure, and outcomes in mechanically ventilated patients without ARDS. Methods: Secondary analysis from 1,705 mechanically ventilated patients enrolled in a clinical study that examined outcomes associated with the use of early lung-protective mechanical ventilation. The primary outcome was mortality and the secondary outcome was the incidence of ARDS. Multivariable modelswere constructed to: define the association between pulmonary mechanics (driving pressure, plateau pressure, and compliance) and mortality; and evaluate if driving pressure contributed information beyond that provided by other pulmonary mechanics. Results: The mortality rate for the entire cohort was 26.0%. Compared with survivors, non-survivors had significantly higher driving pressure [15.9 (5.4) vs. 14.9 (4.4), P=0.005] and plateau pressure [21.4 (5.7) vs. 20.4 (4.6), P=0.001]. Driving pressure was independently associated with mortality [adjusted OR, 1.04 (1.01-1.07)]. Models related to plateau pressure also revealed an independent association with mortality, with similar effect size and interval estimates as driving pressure. There were 152 patients who progressed to ARDS (8.9%). Along with driving pressure and plateau pressure, mechanical power [adjusted OR, 1.03 (1.00-1.06)] was also independently associated with ARDS development. Conclusions: In mechanically ventilated patients, driving pressure and plateau pressure are risk factors for mortality and ARDS, and provide similar information. Mechanical power is also a risk factor for ARDS.