WEAN SAFE (WorldwidE AssessmeNt of Separation of pAtients From ventilatory assistancE) is a multi-centre, prospective, observational, 4-week inception cohort study being carried out by the Acute Respiratory Failure section of ESICM. Weaning represents a challenge for intensivists and patients spend a considerable amount of time in being liberated from mechanical ventilation. While guidelines do exist on the classification of weaning, a recent study has shown that these may not be applicable to all patients. Moreover, different practices exist in regard to weaning procedures. WEAN SAFE will prospectively assess the burden of, management and spectrum of approaches to weaning from ventilation, in patients that require invasive mechanical ventilation for any reason, for a time period of at least 24 hours.

The purpose of this study is to describe, in a large population of ICU patients the burden of, management and spectrum of approaches to weaning from ventilation, in patients that require invasive mechanical ventilation for any reason, for a time period of at least 24 hours. It will answer the following questions:

• What are the current approaches taken to wean patients from invasive mechanical ventilation?
• What is the frequency of delayed weaning from invasive mechanical ventilation?
• What are the factors that are used to determine when patients are in the weaning phase?
• What are the barriers to effective weaning from invasive MV?
• What factors (patient, institutional, medical practice) contribute to failed attempts to wean from invasive mechanical ventilation?
• What is the impact of premorbid conditions on weaning from invasive MV?
• What is the utility of existing classifications for weaning from invasive MV?
• What is the impact of early versus delayed and/or failed weaning from invasive MV?

Patients will be screened for the study when undergoing mechanical ventilation and admitted in the ICU.

Day 1 will be defined as the first day when IMV commences Day 2 commences at 6-10am (fixed time point each day per ICU practice) after IMV commences. Patients undergoing invasive mechanical ventilation on the morning of day 1 will be screened for the study Patients still undergoing IMV on Day 2, will be enrolled in the study Patients not undergoing invasive mechanical ventilation or liberated from invasive mechanical ventilation on day 1 will be re-evaluated daily for the presence of inclusion criteria.

Inclusion Criteria:

Screening: all patients admitted in the ICU and aged >16 will be screened daily

- A patient will be included if he/she is undergoing Invasive mechanical ventilation on the second morning (between 6am and 10 am) after initiation of mechanical ventilation or after ICU admission (if ventilation was already in place).

Exclusion Criteria:

• Lack of informed consent (where required)
• Patients already present in the ICU at the beginning of the study, independently of the form of ventilatory support

Due to the observational nature of the present study, patients enrolled in other observational/interventional study CAN be enrolled in the present study.

We aim to collect a large "convenience sample", with > 5,000 patients. Based on the LUNG SAFE data (NCT02010073; JAMA, 2016 Jul 19;316(3):347), we can estimate to enroll about 11 patients invasively ventilated on Day 2 following intubation per participating ICU in a 4 week period. We are therefore targeting the enrollment of 500 registered ICUs (considering a 10% dropout)