The investigators now propose to conduct a third international study of mechanical ventilation, 6 years after the 2nd study and 12 years after the original. This will again be a prospective, multicenter single-cohort study, which will enroll consecutive patients who have received mechanical ventilation for at least 12 hours during a 1-month period, and will follow each patient for the duration of mechanical ventilation, up to 28 days. With this 3rd study the investigators aim: 1) to determine if the observed changes that the investigators reported previously are maintained over time; 2) to evaluate if the changes implemented have impacted outcomes; 3) to analyze some aspects related to withdrawal of mechanical ventilation; and implementation non-invasive positive pressure ventilation; and 4) to evaluate what differences may occur between geographical areas.