Non Invasive Ventilation in Abdominal Postoperative Period

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