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.

Classically lung elastance and transpulmonary pressure are measured from the difference in tidal variations of airway pressure subtracted by tidal variations in esophageal pressure divided by the tidal volume (Method 1). This requires the presence of a esophageal balloon catheter which is cumbersome and costly.

In this study values obtained as described in Method 1 above are compared to values obtained with a new method in which a PEEP-step is performed with a size which corresponds to the tidal volume which the patient is ventilated with. Measurements using Method 1 and 2 are performed in anesthetized patients prior to major surgery.

Inclusion Criteria:

• Patient undergoing major surgery during anesthesia and muscle relaxation

Exclusion Criteria:

• Patient with chronic obstructive lung disease

Patients which are anesthetized and muscle relaxed and are planned to undergo major surgery