Acute respiratory failure may occur early in the postoperative course, requiring endotracheal intubation and mechanical ventilation in selected patients, thus increasing morbidity and mortality and prolonging intensive care unit (ICU) and hospital stay.We will perform a multicenter, prospective, randomized clinical trial to compare the efficacy of non invasive ventilation (NIV) which associated pressure support ventilation (PSV: 5 to 15 cmH2O) and positive end expiratory pressure (PEEP: 5 to 10 cmH2O) with standard oxygen therapy in the treatment of postoperative acute respiratory failure. We also set out to examine the hypothesis that early application of NIV may prevent intubation and mechanical ventilation in patients who develop acute respiratory failure after abdominal surgery.

The Non-Invasive Ventilation After Surgery (NIVAS) is an investigator-initiated, multi-center, stratified, two-arm parallel-group trial with a computer-generated allocation sequence and electronic system based randomization. The study protocol and statistical analysis plan were approved for all centers by a central Ethics Committee (France) according to French law.The NIVAS study is conducted in accordance with the declaration of Helsinki and was registered on August 2013.All centers have a long experience with NIV (more than 10 years of NIV use for ARF, and more than 5 years of NIV use for ARF following abdominal surgery). Randomization will stratified by department, age (less or more 60 years), site of surgery (upper or lower abdominal) and according to the presence or absence of postoperative epidural analgesia as this may influence outcomes. Treatment assignments will concealed from patients, research staff, the statistician, and the data monitoring and safety committee.

Inclusion Criteria:

Eligibility :

• age of more than 18 years
• scheduled for elective or not elective abdominal surgery requiring laparotomy or laparoscopy and general anesthesia.

Inclusion :

• acute respiratory failure occurring within the seven days of the surgery procedure which is defined as presence and persistence for at least 30 min and at least one of the two followings: 1) a respiratory rate of more than 30 breaths per minute and 2) clinical signs suggestive of respiratory muscle fatigue, increased work of breathing, or both, such as use of respiratory accessory muscles, paradoxical motion of the abdomen, or retraction of intercostal spaces
• hypoxemia defined by a PaO2 lower than 60 mmHg in ambient air or lower than 80 mmHg under 15 liters O2 or an arterial O2 saturation by pulse-oximetry (SpO2) lower than 90% (PaO2/FiO2< 200 mmHg).

Exclusion Criteria:

• Emergency procedure surgery (operation that must be performed as soon as possible and no longer than 12 hours after inclusion in the study)
• previous recruitment into another trial.
• Cardiopulmonary arrest
• Glasgow coma scale <8
• Absence of airway protective gag reflex
• Upper airway obstruction
• Pregnancy.
• Patients who refuse to undergo endotracheal intubation, whatever the initial therapeutic approach
• Chronic home non invasive ventilation