Sleep's deficiencies are very common in intensive care. Mechanical ventilation is a known factor in this deterioration.The investigators hypothesize that close-loop ventilation mode (Intellivent-ASV) is able to minimize sleep deterioration, adjusting ventilation to the patient needs.

In intensive care, conventional mechanical ventilation (pressure support) generates apneas and asynchronies during sleep. Intellivent-ASV would be able to avoid apneas, providing controlled cycles when respiratory rate become too low. Moreover, the constant adjustment of ventilatory parameters to the patient needs would avoid asynchronies between the ventilator and the patient ventilatory drive.

Inclusion Criteria:

• patient under invasive mechanical ventilation since at least 6 hours and for expected at least 48 hours duration, including a continuous period of 24h, from 2 p.m. to 2 p.m. the next day.
• Age > 18 years
• Body Mass Index < 40
• informed consent signed by the family

Exclusion Criteria:

• patient requiring neuo-muscular blocking agent or deep sedation enough to abolish spontaneous ventilatory effort
• patient with encephalopathy regardless of origin
• Patient with Glasgow coma scale score < 8
• Patient abusing of drug or alcohol
• patient with a contraindication for placement of a nasogastric tube such that sufferers of esophageal or gastric ulcer, tumors, diverticulitis or bleeding varices or patients with sinusitis epistaxis or having recently been operated on the nose or pharynx
• Patient with bleeding disorders
• Patient with unstable respiratory situation as defined by a arterial oxygen partial pressure and inspired oxygen fraction ratio (PaO2/FiO2) < 100 mmHg with positive end expiratory pressure (PEEP) > 12 cmH2O
• Patient with unstable hemodynamic situation as defined by Systolic Blood Pressure (SBP) < 75 mmHg despite a therapeutic optimization
• Inclusion in another research protocol submitted to consent