 Classically lung elastance and transpulmonary pressure are measured from the difference in tidal variations of airway pressure subtracted by tidal variations i esophagus pressure divided by the tidal volume. This requires the presence of a esophageal balloon catheter which is cumbersome and costly. In this study values obtained as described above are compared to values obtained with a new method in which a stepwise increase in positive endexpiratory pressure PEEP is performed with a size which corresponds to the tidal volume which the patient is ventilated with. These measurements are performed in anesthetized patients prior to major surgery. 