Positive inspiratory pressure (PIP), intratracheal pressure (Ptrach), mean airway pressure (MAP), PEEP, SpO 2 , ET-CO 2 , respiratory rate and V Te were measured. Ptrach was measured with a pressure transducer placed at the distal end of the endotracheal tube. Blood samples were drawn for the determination of the PaO 2 , PaCO 2 and pH. Static compliance (C stat ), R rs and peak expiratory flow rate (PEFR) were measured using the AVEA ventilator (Cardinal Health, Yorba Linda, CA, USA) according to the manufacturer's manual. In summary, R rs was defined by the ratio of the airway pressure differential to the inspiratory flow 12 ms prior to the end of inspiration. Lung resistance (R lung ) was defined by the ratio of the tracheal pressure differential to the inspiratory flow 12 ms prior to the end of inspiration.