This trial evaluates tracheal pressure values in intubated intensive care unit patients during continuous positive airway pressure without any ventilatory support, automatic tube compensation and assisted spontaneous breathing.

Aim of this trial is to investigate if there are any significant differences between airway and tracheal pressure values during continuous positive airway pressure (CPAP) ventilation. For this purpose, a tracheal pressure measurement catheter is inserted into the tracheal tube and the obtained values are compared with the corresponding airway pressure measured on the ventilator. To further evaluate the impact of mild respiratory support automatic tube compensation and assisted spontaneous breathing with 4 cmH2O will be applied and measured pressure values compared as well.

We hypothesize that tracheal pressure will be significantly lower than airway pressure values during inspiration, which represents the primary outcome measure. Secondary outcome parameters include comparison of expiratory and mean pressure values of airway and tracheal pressure. Additionally, effects of mild respiratory support will be evaluated as well.

Measurement of inspiratory tracheal pressure might allow to calculate the pressure drop between the airway pressure at the Y-piece of the ventilator and the pressure at the trachea. Currently it is not known, if this pressure drop is significant during CPAP, which represents the rationale to perform this pilot study. In a second step it would be possible to determine if the recorded pressure drop can be used as a surrogate parameter for the respiratory drive in terms of a risk assessment for the development of patient self-inflected lung injury.

Inclusion Criteria:

• Male and female subjects ≥ 18 years
• Intubated patient during CPAP without pressure support
• Informed consent

Exclusion Criteria:

• Female subjects known to be pregnant
• Known participation in another clinical trial
• Critical pulmonary state (paO2/FiO2 ratio <100)