Introduction: At present, the best spontaneous breathing trial (SBT) during weaning from mechanical ventilation is a 30-min test with pressure support (PSV) 8 cmH2O without positive end-expiratory pressure (PEEP). There is a debate about the possible collapse of some alveolar units during such SBT and during extubation with continuous suctioning. A few experiences show extubation without suctioning as feasible and safe. Lung ultrasound is a non invasive and useful exploration tool to assess the lung aeration.

Hypothesis: Techniques aimed at preserving lung volume during SBT and extubation can yield higher rates of successful extubation. The preserved lung volume of each SBT and extubation strategy can be assessed by using lung ultrasound.

Primary objective: To define the rates of successful extubation in two extubation approaches aiming at different levels of lung volume preservation: standard SBT (30-min PSV 8 cmH2O without PEEP followed by extubation with continuous suctioning) versus experimental SBT (PSV8+ PEEP 5 cmH2O followed by extubation without suctioning). To define the lung aeration levels using the modified Lung Ultrasound Score (LUS) of each SBT strategy.

Secondary objectives: Reintubation rate, ICU and hospital stays, and mortality in each group. To define the diaphragm and intercostal thickness and thickening fraction in different levels of lung volume preservation.

Design: Prospective, multicenter, randomized study. Two opposing extubation strategies are compared in randomly assigned patients.The level of aeration is assessed using lung ultrasound.

HYPOTHESIS Techniques aimed at preserving lung volume during SBT and extubation can yield higher rates of successful extubation. Lung Ultrasound Score (LUS) might be lower in techniques aiming to preserve lung volume suggesting less lung collapse.

METHODS

Patients with inclusion criteria and none exclusion criteria will be randomized to the follow strategies:

• Standard: PSV 8 cmH2O, PEEP 0 cmH2O for 30 minutes and, when successful, followed by extubation with continuous suctioning.
• Lung volume preservation: PSV 8 cmH2O, PEEP 5 cmH2O for 30 minutes and, when successful, followed by direct extubation without suctioning.

The randomization will be done with the built-in tool of the RedCap® Platform with computerized random number tables and blocks of n patients for each hospital. The investigators of each center will have a profile and a password to log into the RedCap and proceed with randomization of each patient. The investigator of each center will have access only to the data and randomization of his/her center.

In extubation failure patients (those who does not tolerate the SBT or not extubated), the attending physician will decide on the treatment, either support with non-invasive ventilation or with high flow nasal cannula, or reintubation.

Patients who present extubation failure will not be randomized in later SBTs.

During the SBT, interventions that the physician considers necessary to monitor the success of the test, such as echocardiography or thoracic ultrasound, may be performed. In the event that the physician considers that the findings of these tests do not guarantee successful extubation despite fulfillment of extubation criteria according to the study protocol, the attending physician's decision will prevail over the study protocol. In these cases, it will be recorded in the case report form (CRF) as extubation failure due to "other causes of weaning failure".

Not all patients and participating centers will collect data from the lung, diaphragm and intercostal ultrasound assessment. Only those patients that showed interest and proved ultrasound skills, will participate in the ultrasound part of the nested study.

Those patients included in the Ultrasound assessment part, an ultrasonographic exploration will be performed at different times of the SBT and extubation: before starting the SBT, at the final of the SBT and after extubation.

To proof the hypothesis related to the LUS and considering a minimum difference of 1 point (LUSm ranges from 0 to 24 points), we anticipate that 93 in each arm are required .

OBJECTIVES:

Primary: To determine the rate of successful extubation in two opposite weaning strategies.

Secondary:To determine the LUS in two opposite weaning strategies. To determine the ICU stay, hospital stay, hospital survival, and 90-day survival in the two groups. To identify the causes of extubation failure (clinical and ultrasonographic).

Exploratory:To determine the diaphragm and intercostal thickness and thickening fraction in the two groups. To describe patterns of LUS, diaphragmatic and intercostal muscles in patients who fail weaning. To assess changes in LUS during SBT and extubation specifically in posterior-basal regions. To describe diaphragmatic thickening fraction during P0.1 and Pocc maneuvers.

Inclusion Criteria:

• Patients> 18 years who meet weaning criteria (see below)
• More than 24 hours of mechanical ventilation (MV)
• Signed Informed Consent by a substitute decision maker (SDM).

Weaning Criteria:

• Suitable cough (Ability to raise secretions to the endotracheal tube) (or Maximal inspiratory pressure (MIP) < -15 cmH2O).
• Absence of excessive secretions (<3 aspirations in the last 8 hours).
• Resolution or improvement of the pathology that led to intubation.
• Clinical stability (Heart Rate (HR) <140 bpm, Systolic Blood Pressure (SBP) 90-160, without vasopressors or at minimum doses).
• Adequate oxygenation (SatO2> 90% with Inspiratory Fraction of oxygen (FiO2) <0.4).
• Adequate ventilatory mechanics (Respiratory rate (RR) <35 rpm, Tidal Volume (TV) > 5 ml / kg, RR / TV <100 rpm/l).
• Confident awareness level (Glasgow Coma Scale (GCS)> 13).

Exclusion Criteria:

• tracheostomy, do-not-reintubate orders, decision of the responsible physician (e.g., due to a preference for a particular weaning technique according to the underlying pathology), absence of informed consent, mental incapacity without legal representation.
• For ultrasound assessment: skilled explorer not present at the time of the SBT, inadequate ultrasound window. Known diaphragmatic paralysis.

If any researcher is interested on exploratory analysis, it should be presented to the principal investigator to get the approval for it.