Several studies investigated the role of specific clinical predictors of weaning success, but it is determined by a combination of different aspects that can result in success or failure. Indeed, unresolved lung disease, cardiac dysfunction, loss of respiratory and core muscle strength can play a role in a failure weaning to mechanical ventilation (MV). The investigators hypothesized that a combined score that include heart, lung, and respiratory muscle ultrasound (US) evaluation could be able to predict the ability of weaning success. Furthermore, it will be described weather the days of MV before weaning trial may affect the relevance of each clinical variable evaluated.

Critically ill patients undergone at least 48 hours of MV and ready to spontaneous breathing trial (SBT) will be included in the study. The spontaneous breathing trial is performed in pressure support ventilation with a clinician-set positive end expiratory pressure (PEEP) ≤ 5 cm H2O and FiO2< 40%. In addition to the parameters traditionally used for the evaluation of weaning (RSBI), the investigators will perform ultrasound evaluation of diaphragm, lung parenchyma, cardiac function, and the strength of the hand grip.

Investigators will evaluate the diaphragmatic parameters (thickening fraction,TF, and diaphragmatic displacement, DD) and TFmax (TF during forced breathing /TF during tidal respiration) to identify the inspiratory reserve. Weaning success is considered as liberation from MV within 72 hours.

Inclusion Criteria:

• aged between 18 and 90 years
• Mechanical ventilation> 48 h
• Reason for ICU admission: medical / surgical / trauma

Exclusion Criteria:

• age under 18
• diagnosis of neuromuscular disease
• tracheostomy
• terminal extubation
• pregnancy in progress -
• previous paralysis of the diaphragm or of a hemidiaphragm
• use of neuromuscular blocking drugs in continuous infusion in the 48 hours preceding the weaning attempt.
• Refusal to participate in the study

mechanically ventilated patients