Early acute lung injury: criteria for identifying lung injury prior to the need for positive pressure ventilation*.

OBJECTIVE: Mortality associated with acute lung injury remains high. Early identification of acute lung injury prior to onset of respiratory failure may provide a therapeutic window to target in future clinical trials. The recently validated Lung Injury Prediction Score identifies patients at risk for acute lung injury but may be limited for routine clinical use. We sought to empirically derive clinical criteria for a pragmatic definition of early acute lung injury to identify patients with lung injury prior to the need for positive pressure ventilation.
DESIGN: Prospective observational cohort study.
SETTING: Stanford University Hospital. PATIENTS: We prospectively evaluated 256 patients admitted to Stanford University Hospital with bilateral opacities on chest radiograph without isolated left atrial hypertension.
INTERVENTIONS: None.
MEASUREMENTS AND MAIN RESULTS: Of the 256 patients enrolled, 62 patients (25%) progressed to acute lung injury requiring positive pressure ventilation. Clinical variables (through first 72 hr or up to 6 hr prior to acute lung injury) associated with progression to acute lung injury were analyzed by backward regression. Oxygen requirement, maximal respiratory rate, and baseline immune suppression were independent predictors of progression to acute lung injury. A simple three-component early acute lung injury score (1 point for oxygen requirement > 2-6 L/min or 2 points for > 6 L/min; 1 point each for a respiratory rate ≥ 30 and immune suppression) accurately identified patients who progressed to acute lung injury requiring positive pressure ventilation (area under the receiver-operator characteristic curve, 0.86) and performed similarly to the Lung Injury Prediction Score. An early acute lung injury score greater than or equal to 2 identified patients who progressed to acute lung injury with 89% sensitivity and 75% specificity. Median time of progression from early acute lung injury criteria to acute lung injury requiring positive pressure ventilation was 20 hours.
CONCLUSIONS: This pragmatic definition of early acute lung injury accurately identified patients who progressed to acute lung injury prior to requiring positive pressure ventilation. Pending further validation, these criteria could be useful for future clinical trials targeting early treatment of acute lung injury.