All Patients who are admitted to ICU and who are on controlled mechanical ventilation for more than 24 hours are eligible for the study (Screening).

A patient must meet all the criteria listed below and show readiness to perform the preinclusion test to participate in the trial:

• Age ≥ 18 years
• Duration of controlled mechanical ventilation ≥ 24h
• Availability of a Infinity V500 ventilator (ready to use)
• Informed consent according to local regulations
• Temperature ≤ 39 °C
• Hemoglobin ≥ 6 g/dl
• PaO2/FIO2 Ratio ≥ 150 mmHg with PEEP ≤16 cmH2O
• Ability to breath spontaneously

A patient meeting any of the exclusion criteria listed below must be excluded from participating in the trial.

• Participation in another interventional trial within the last four weeks before enrollment in this trial
• Peripheral neurological disease associated with impairment of the respiratory pump
• Muscular disease associated with impairment of the respiratory pump
• Instable thorax with paradoxical chest wall movement
• Planned surgery under general anesthesia within 72 hours
• Difficult airway/intubation
• Existing tracheotomy at time of randomization
• Expected survival < 72 hours
• Home mechanical ventilation or on chronic oxygen therapy
• Suspected pregnancy