We hypothesize that the ventilatory mode Bilevel Positive Airway Pressure without any synchronization (BIPAPasynchro) may facilitate the weaning process of patients intubated with acute hypoxiemic respiratory failure (AHRF) by obviating the problem of patient-ventilator asynchrony. In order to prove this hypothesis a large randomized controlled study should be perfromed comparing BIPAPasynchro versus pressure support ventilation (PSV), the most widely used ventilatory mode during the weaning process. In order to do so, a feasibility trial to demonstrate the ICU personnel can effectively use a non-standard ventilatory mode should be first performed. The objective of our study is, thus, to demonstrate the feasibility of using BIPAasynchro in the Lausanne Adult ICU.

Bilevel Positive Airway Pressure without any synchronization (BIPAPasynchro) ventilation is a ventilatory modality that guarantees a minimal mandatory minute ventilation, even in deeply sedated patients, and allows free spontaneous breathing as soon as possible, without requiring synchronization between the patient and the ventilator. The hypothesis is that, as it obviates the problem of patient-ventilator asynchrony, it could reduce, compared to pressure support ventilation (PSV), the need of sedation, decrease diaphragmatic atrophy and accelerate the liberation from mechanical ventilation (weaning phase) without exposing the patients to further risks. Data seems to suggest a potential benefit of BIPAPasynchro over PSV, but no large randomized controlled trials have been performed to compare the two techniques; however, this cannot be done after first demonstrating that it is feasible to use BIPAPasynchro in the weaning process from mechanical ventilation in the intensive care unit.

The present project aims at assessing the feasibility of using a standardized BIPAP weaning strategy. It is thus a feasibility trial that assesses the adherence to the use of the mode. It is a randomized trial with two parallel groups in which we will compare the percentage of time effectively spent in the assigned mode, either BIPAP asynchro (intervention group) or PSV (control group), since the first switch from assist-control ventilation to assisted ventilation.

The study primary endpoint is the percentage of patients who spent at least 65% of the time (a priori-chosen cut-off) in the assigned mode (either BIPAPasynchro or PSV mode) since the first switch to assisted ventilation until successful liberation from mechanical ventilation. Liberation from mechanical ventilation (successful weaning) is defined as follows: 1) for intubated patients, we consider the patient weaned from ventilation when extubated without reintubation within 72 hours. 2) For tracheostomized patients, we consider the patient weaned from ventilation as soon as ventilated less than 12h over 24h during three consecutive days.

The secondary endpoints are divided in other-feasibility endpoints, safety endpoints and exploratory endpoints.

The study secondary feasibility endpoints are:

1. the proportions of participants who are switched to the non-assigned mode (cross-over from one study group to the other). Concretely, this refers to the situations where the patients in the PSV group are ventilated in BIPAPasynchro and the patients in the BIPAPasynchro group are ventilated in PSV.

2. The percentage of time spent in the non-assigned ventilatory mode since patient inclusion;

3. reasons for cross-over;

4. physicians refusal rate of patient enrolment;

5. reasons of physicians refusal if applicable;

6. recruitment rates.

   Secondary safety endpoints

   The study secondary safety endpoints are:

7. pneumothoraxes rate;

8. unplanned extubation rate;

9. rate of severe respiratory acidosis (pH < 7.20);

10. rate of severe respiratory alkalosis (pH > 7.55);

11. ventilation acquired pneumonia (VAP) rate (13).

    Secondary exploratory endpoints

    The study secondary exploratory endpoints are:

12. ventilator-free-days at day 28 from intubation (VFDs-28);

13. ventilator-free-days at day 28 from randomization;

14. duration of invasive mechanical ventilation between randomization and successful weaning, as defined in § 2.2.1;

15. duration of invasive mechanical ventilation between randomization and successful weaning, defined as no reintubation (or reventilation) during 7 days after extubation

16. number of tracheostomized patients during the weaning process;

17. number of patients matching the criteria for difficult or prolonged weaning (14).

18. length of ICU stay (censored at day 90 after randomization);

19. ICU-free days at day 90 from randomization;

20. length of Hospital stay (censored at day 90 from randomization);

21. hospital-free days at day 90 from randomization;

22. proportion of days with RASS less or equal -2 (for almost 50% of daily assessments) during invasive mechanical ventilation;

23. proportion of days with sedation during invasive mechanical ventilation;

24. proportion of days with neuromuscular blocking agents administration for ventilation facilitation during invasive mechanical ventilation;

25. ICU mortality (censored at day 90 from randomization);

26. hospital mortality (censored at day 90 from randomization).

This is a prospective, open-label, parallel-group, randomized feasibility trial taking place in the Adult ICU of the University Hospital of Lausanne, Switzerland. Due to the nature of the research, this is an open-label study. Patients will be randomized with a 1:1 ratio for receiving either BIPAPasynchro or PSV as soon as switching to assisted ventilation is considered as possible by the attending physician.

Inclusion Criteria:

• Intubated ICU patient with acute respiratory failure;
• PaO2-FiO2 ratio of less than 300 mmHg (40 kPa) at least one hour after intubation;
• control or assist-control ventilation;
• expected duration of mechanical ventilation of more than 24 hours;
• clinician in charge considers that the patient can be switched to assisted ventilation (weaning phase start);
• informed consent obtained by the patient himself / legal representative or authorization received from independent physician

Exclusion Criteria:

• less than 18 years old;
• pregnant women (because of very different respiratory mechanics);
• severe obesity (BMI > 40 kg/m2);
• known obstructive pulmonary disease;
• expected death within one week or very poor prognosis with end-of-life care decision expected/treatment withdrawal;
• neurological disorders heavily influencing breathing pattern, like suspected or proven hypoxic brain injury, spinal injury above C8, severe traumatic brain injury, polyneuropathies (ex. Guillain-Barré, myasthenia gravis);
• home non-invasive ventilation prior to ICU admission, except CPAP for obstructive sleeping apnoea syndrome;
• tracheostomised at ICU admission;
• suspected or proven broncho-pleural fistulas;
• extracorporeal membrane oxygenation (ECMO) treatment;
• ICU admission for major burns;
• enrolment in other trial with competitive outcomes or treatment strategies;
• Known opposition to research participation if patient is not able to consent (eg patient with refused GC)