Airway pressure-time (P-t) curve and stress index (SI) assessment have been proposed to guide the mechanical ventilation settings and minimize ventilator-induced lung injury.

The stress index (SI), which has been proposed to guide the mechanical ventilation settings and minimize ventilator-induced lung injury. It reflects the change of respiratory compliance during inspiration. Value of SI equals to 1 that indicates a constant compliance, whereas values lower and higher than 1 indicate increase and decrease of compliance over inspiratory time, suggesting tidal recruitment and tidal hyperinflation, respectively. Based on the different values of SI showing different shapes, SI of straight curve equals to 1, SI of concave curve lower than 1 and convex curve higher than 1, the investigators speculated that the SI value could be reliably and accurately estimated by visual inspection of the P-t curve.

Inclusion Criteria:

• aged 18 years or older; intubated and mechanical ventilated by volume-control ventilation with constant flow;

Exclusion Criteria:

• evidence of active air leak from the lung, including bronchopleural fistula, pneumothorax, pneumomediastinum, or existing chest tube; evidence of the stiff chest wall, such as existing the pleural effusion, intra abdominal hypertension, chest injuries and abdominal injuries.

intubated and mechanical ventilated by volume-control ventilation with constant flow