This study is an extension of the Spanish Initiative for Epidemiology, Stratification and Therapies of Acute respiratory failure (SIESTA) Network.

The present study is aimed to establish the epidemiological characteristics and clinical outcomes of mechanically ventilated patients with acute hypoxemic respiratory failure [defined as a PaO2/FiO2 ≤300 mmHg on positive end-expiratory pressure (PEEP) of 5 cmH2O or more, and FiO2 of 0.3 or more] admitted in a network of Spanish hospitals.

The present study is aimed to establish the epidemiological characteristics and clinical outcomes of adult mechanically ventilated patients with acute hypoxemic respiratory failure [defined as a PaO2/FiO2 ≤300 mmHg on positive end-expiratory pressure (PEEP) of 5 cmH2O or more and FiO2 of 0.3 or more] admitted in a network of Spanish hospitals. Although there are few previous published observational studies examining the incidence and mortality of patients with acute respiratory failure and ARDS, there are no studies specifically assessing the epidemiological characteristics, patterns of ventilation and clinical outcomes in patients with acute hypoxemic respiratory failure in the current era of lung protective ventilation.

Since the study is prospective, with consecutive collection of clinically relevant data from patients and with the participation of several ICUs from different geographical regions of Spain, the findings would be highly generalizable. The study is aimed to improve the knowledge on the epidemiology and outcome of ventilated patients, to identify the percentage of patients developing ARDS under the current definition, to validate a bedside scoring system developed by us for stratification of lung severity, and to examine the prognosis of hypoxemic respiratory failure, and risk factors associated with fatal outcome.

Inclusion Criteria:

• Age ≥18-year old.
• Endotracheal intubation and mechanical ventilation, independent of whether the need for ventilatory support is shorter or longer than 24 hours. Only patients receiving invasive mechanical ventilation can be included, although patients could have been on non-invasive ventilation before intubation.
• PaO2/FiO2 ≤300 mmHg on invasive mechanical ventilation with a PEEP of 5 cmH2O or more, and with a FiO2 of 0.3 or more.

Exclusion Criteria:

• No patients should be excluded (if they meet all the inclusion criteria), regardless of the underlying disease, estimated life expectancy, or duration of invasive mechanical ventilation.

All consecutive patients admitted to participating ICUs will be screened daily. Only patients meeting inclusion criteria for acute hypoxemic respiratory failure (as defined above) will be enrolled into the study.

Patients' data will be anonymized and recorded in a case report form (CRF) specifically designed for this study. Data will be presented globally at the end of the study