Conflict of interest: T. Raveling has nothing to disclose. Conflict of interest: J. Kort has nothing to disclose. Conflict of interest: G. Bladder has nothing to disclose. Conflict of interest: W. Windisch reports grants from Weinmann Germany, Vivisol Germany, Heinen und Löwenstein Germany, VitalAire Germany and Philips/Respironics USA, during the conduct of the study; personal fees for lectures from companies dealing with mechanical ventilation, outside the submitted work. Conflict of interest: P.J. Wijkstra reports grants and personal fees from Philips and Resmed, grants from Vital Air, Vivisol and Goedegebuure, personal fees from Synapse and Bresotec, outside the submitted work. Conflict of interest: M.L. Duiverman reports grants and personal fees for lectures from Philips BV, personal for lectures and advisory board work fees from Resmed Ltd, grants from Vivisol BV and Fisher and Paykel Ltd, outside the submitted work.