The main hypothesis are:

1. Passive and Active-Passive airway conditioning devices reduce the incidence of ventilator associated pneumonia
2. Active-Passive airway conditioning devices reduce the incidence of endotracheal tube obstruction
3. Nurses' workload is reduced with Passive and Active-Passive airway conditioning devices

For all Three lines of the study we record Clinical Pulmonary Infection score and Airways Care Score, SOFA (Sequential Organ Failure Assessment), sedation strategy, Glasgow Coma Score and clinical data.

Inclusion Criteria:

• Patients mechanically ventilated with PaO2/FiO2 lower than 300
• Age higher than 18 years
• Invasive mechanical ventilation
• Endotracheal intubation or tracheostomy for more than 24 hours

Exclusion Criteria:

• Non invasive ventilation
• Severe ARDS (PaO2/FiO2 lower than 100, or PaCO2 higher than 60 mmHg)
• Inefficient cough
• Head Trauma
• Spinal cervical trauma
• Chest trauma
• Pregnancy
• Expectance of poor survival within 72 hours
• Congenital airway disease
• Immunosuppression
• Supraglottic aspiration devices