Protocol for monitoring
Airway pressure (Paw) was measured with a proximal sampling line placed just after the endotracheal tube, along with a self-calibrating pneumotachometer (Viasys Variflex 51,000–40094; Conshohocken, PA). One of the three esophageal catheters were used, based on the size of the patient (Carefusion, Avea SmartCath 6, 7, or 8 Fr). The amount of air inflated into esophageal balloon was determined before each measurement using a previously validated calibration algorithm [