Accuracy of Plateau Pressure and Stress Index to Identify Injurious Ventilation in Patients with Acute Respiratory Distress Syndrome

Background: Guidelines suggest a plateau pressure (Pplat) of 30 cm H2O or less for patients with acute respiratory distress syndrome, but ventilation may still be injurious despite adhering to this guideline. The shape of the curve plotting airway pressure versus time (StressIndex) may identify injurious ventilation. The authors assessed accuracy of Pplat and StressIndex to identify morphological indexes of injurious ventilation. Methods: Indexes of lung aeration (computerized tomography) associated with injurious ventilation were used as a reference standard. Threshold values of Pplat and StressIndex were determined assessing the receiver-operating characteristics (training set, N = 30). Accuracy of these values was assessed in a second group of patients (validation set, N = 20). Pplat and StressIndex were partitioned between respiratory system (Pplat,Rs and StressIndex,rs) and lung (Pplat,l and StressIndex,l; esophageal pressure; physiological set, N = 50). Results: Sensitivity and specificity of Pplat of greater than 30 cm H2O were 0.06 (95% CI, 0.002-0.30) and 1.0 (95% CI, 0.87-1.00). Pplat of greater than 25 cm H2O and a StressIndex of greater than 1.05 best identified morphological markers of injurious ventilation. Sensitivity and specificity of these values were 0.75 (95% CI, 0.35-0.97) and 0.75 (95% CI, 0.43-0.95) for Pplat greater than 25 cm H2O versus 0.88 (95% CI, 0.47-1.00) and 0.50 (95% CI, 0.21-0.79) for StressIndex greater than 1.05. Pplat,Rs did not correlate with Pplat,l (R-2 = 0.0099); StressIndex,rs and StressIndex,l were correlated (R-2 = 0.762). Conclusions: The best threshold values for discriminating morphological indexes associated with injurious ventilation were Pplat,Rs greater than 25 cm H2O and StressIndex,rs greater than 1.05. Although a substantial discrepancy between Pplat,Rs and Pplat,l occurs, StressIndex,rs reflects Stress Index,L.