Bedside Spirometry for Acute Lung Injury

The diagnosis of Acute Respiratory Distress Syndrome (ARDS) is a syndromic diagnosis that groups together patients who may have very different prognoses and respond differently to the same therapies. Additionally, non-invasive ventilation (NIV) has shown highly contrasting results in the early management of ARDS. One of the predictive criteria for NIV failure is an excessively high tidal volume during non-invasive ventilation. SPIRALI is a pilot study evaluating the relevance of a respiratory physiology parameter, the tidal volume relative to the theoretical ideal body weigh, in the phenotypic classification of non-intubated ARDS patients. In this initial approach, the investigators will compare the tidal volume during high-flow oxygen therapy with the tidal volume obtained under NIV (after applying a settings optimization algorithm). The investigators hypothesize that if tidal volume is linked to each situation, the same patients will exhibit a high tidal volume both during spontaneous ventilation and under NIV.

Inclusion Criteria: * Patient over 18 years of age; * Patient hospitalized in intensive care for less than 24 hours; * Patient with severe hypoxemic acute respiratory failure characterized by a PaO2/FiO2 ratio \< 300 mmHg and \> 150 mmHg under high-flow oxygen therapy at 60 L/min; * Patient able to cooperate with the spirometry test; * Patient able to follow the protocol and having given their informed written consent to participate in the study; * Patient affiliated with the social security system or entitled to benefits; Exclusion Criteria: * Patients with an indication for intubation; * Patients with a contraindication for or who refuse NIV; * Patients with hemodynamic instability requiring vasopressor support greater than 0.25 μg/kg/min of norepinephrine; * Patients with a Glasgow score \< 15; * Patients with hypercapnia (PaCO2 \> 45 mmHg); * Patients with a PaO2/FiO2 ratio \< 150 mmHg; * Patients with cardiogenic pulmonary edema; * Patients who have already undergone a session of NIV in intensive care during this stay; * Patients with chronic respiratory failure (home oxygen therapy or home non-invasive ventilation (excluding indications solely for sleep apnea syndrome)); * Patients who have recently had a pneumothorax; * Patients who have recently undergone eye surgery (e.g., cataract surgery) or throat surgery; * Patients with significant arterial disease: recent heart attack, pulmonary embolism, poorly controlled hypertension despite treatment, etc. * Patients already included in the study; * Pregnant women, women in labor, or women who are breastfeeding; * Patients under guardianship, conservatorship, or deprived of their liberty; * Patients under an activated future protection mandate; * Patients under family authorization; * Patients under judicial protection;