 Airway pressuretime curve Paw-t shape analysis at constant flow ventilation Stress Index, SI is thought to be predictor of lung stress; so the SI coefficient may therefore identify and quantify mechanical stress during ventilation. 1 In experimental studies, the threshold values for SI that best discriminated lungs with signs of Ventilator Induced Lung Injury ranged between 0.9 and 1.1. 2 During EVLP, the isolated lungs are free from the effect of chest wall impairment and represent the effective response of lung parenchyma to ventilatory setting. 