One method for treating intraoperative hypoxia during one-lung ventilation (OLV) is application of PEEP to the dependent lung. However, only a minority of patients benefit from this maneuver. The effect of applied PEEP on oxygenation depends on the relation between the total end-expiratory pressure and the lower inflexion point (LIP) of pressure-volume curve (1). LIP during OLV can be determined with super-syringe technique, but is too complicated for routine operating room use. An alternative is the constant-flow method which is easy and widely used in intensive care settings (2). The investigators goal was to confirm that the constant-flow method as applied by an intensive care ventilator works during OLV.