Patients who are intubated and mechanically ventilated for acute respiratory failure in the Intensive Care Unit (ICU) are at some point eligible for weaning. The common way to wean them from mechanical ventilation is to screen criteria for feasibility and, if present, to test feasibility by performing spontaneous breathing trial. This latter can be done either by setting a low pressure support level (expected to compensate the airflow resistance due to endotracheal tube) or by allowing the patient to breathe spontaneously through the tube without any support from the ventilator. Combination of low pressure assistance strategy (7 cm H2O) and positive expiratory pressure (PEP) of 4 cm H2O is the strategy used in our unit. Such a low pressure support level should actually result in a real assistance and, hence this is not the real spontaneous breathing capacity that is tested. Some ICU ventilators offer the option of compensating for the airflow resistance due to endotracheal tube, automatic tube compensation (ATC). Therefore, investigators aimed at comparing in patients ready to wean the usual procedure in our ICU and the ATC mode. In the ATC arm, the patients are breathing spontaneously through the endotracheal tube and are connected to the ventilator set at inspiratory pressure support of 0 cm H2O, PEP 4 cm H2O and ATC on.

Two parallel arms depending on the order of allocation of each mode: pressure support 7 cm H2O + PEP 4 cm H2O then ATC or the opposite. The primary endpoint is the power of the work of breathing. The hypothesis is that the power of the work of breathing is greater in ATC than in the usual procedure, and hence this latter is a real ventilator support.

Inclusion Criteria:

• age 18 years or more
• intubated and mechanically ventilated for at least 24 consecutive hours
• staying in the medical ICU at the Croix Rousse Hospital, Lyon, France
• pressure support ventilation 10-15 cm H2O, total respiratory rate 25-35 breaths/min, expired tidal volume 6-8 ml/kg predicted body weight
• meeting criteria for spontaneous breathing trial (able to answer simple questions, no ongoing intravenous sedation, norepinephrine ≤ 1 mg/H, dobutamine ≤ 20 mg/h, fraction of inspired oxygen (FIO2 ≤ 50%), PEP ≤ 5 cm H2O, respiratory rate ≤ 35 breaths/min, saturation in oxygen (SpO2) ≥88%)
• under Dräger Evita XL ou V500 ICU ventilator
• agreement to participate from the patient or next of kin

Exclusion Criteria:

• Chronic respiratory failure under long term home oxygen therapy and/or non invasive ventilation before ICU admission
• Tracheotomy
• nasogastric tube contra-indicated
• thoracic tube in place
• no agreement to participate
• under justice protection
• deprived of freedom
• pregnant or breastfeeding
• not affiliated to social insurance
• involved into another study that may interfere with present study