Ventilator-induced lung injury is a common complication. The latest and most noticeable theory of its pathogenesis is called 'ergotrauma' by Gattinoni in 2016. The theory uses ventilator-imposed 'energy' or 'power' to encompass several known forms of injury-inducing factors such as pressure,volume, flow, rate, etc. However, to quantify power imposed by ventilator is no easy task in clinical practice. So, Gattinoni proposed a mathematical formula for easy power calculation. However, Gattinoni did not compare the difference between various etiologies of acute lung injury. We will enroll 100 patients (50 with acute respiratory distress syndrome and 50 with normal lung). The ventilator-imposed power at various tidal volume (6, 8, 10 ml/Kg) and positive end-expiratory pressure (5, 10 cmH2O) will be calculated by the formula. The area enclosed by hysteresis of pressure-volume curve, and hence the work it implies, will be measured as a standard. Our study will aim to compare the formula in different patient groups and in Taiwanese people.

Inclusion Criteria:

• Intubated patients aged 20 to 90 years old

Exclusion Criteria:

• Fraction of inspired oxygen (FiO2) higher than 60%
• Acute physiology and chronic health evaluation (APACHE) II score more than 30
• Plateau pressure or peak airway pressure more than 30 cmH2O
• High risk for barotrauma
• Unstable hemodynamic status
• Under airway pressure release ventilation or high frequency oscillation ventilation therapy
• Under extra-corporeal membrane oxygenation support
• On prone position

Single ICU in one teaching hospital