The primary objective is to test whether variable as compared to non-variable (conventional) PSV reduces the duration of mechanical ventilation.

The secondary objectives are to test whether variable as compared to non-variable pressure sup-port ventilation:

• shortens the total time of mechanical ventilation,
• shortens length of stay in the ICU and in-hospital
• reduces mortality
• improves lung function
• improves patient comfort;
• reduces organ failure
• reduces the need for noninvasive ventilation and reintubation;
• reduces the number of interventions of the ICU personal in the mechanical ventilator;
• increases the variability of respiratory parameters of the breathing pattern

Primary Endpoint: Weaning time defined as time of randomization to successful extubation.

Secondary Endpoints

• Total time of mechanical ventilation
• Time from randomization to first extubation
• Time from randomization to fulfillment of extubation criteria
• Time between fulfillment of extubation criteria and extubation
• ICU length of stay, in-hospital length of stay
• ICU and in-hospital-mortality, mortality at day 90 and 6 month
• PaO2/FIO2, PaCO2
• Minute ventilation
• Mean tidal volume ( VT), mean pressure support, mean airway pressure, mean peak inspiratory pressure
• Inspiratory airway occlusion pressure at 100 ms (P0.1)
• Visual analogue scale for breathing comfort
• Cumulative amount of sedative and analgesic drugs
• SOFA-Score
• Incidence of reintubation
• Incidence of noninvasive ventilation (NIV)
• Postextubation length of NIV
• Ventilator-free-days (28-days)
• Number of changes in mean pressure support by ICU personnel
• Coefficients of variation of VT, pressure support, respiratory rate, inspiratory and expiratory times