Comparison of Two Ventilator Mode During the Night: New Strategy of Mechanical Ventilation Weaning

Inclusion Criteria: * The patient and/or legal representative of the patient has provided a written informed consent before inclusion in the study * The patients is hospitalized in respiratory and critical care unit (university hospital of AMIENS, FRANCE) * the patient is mechanically ventilated (ventilator model : puritan-bennett B840) * Pulmonary disease,chronic obstructive (Spirometry and Blood Gas Analysis in chronic state before admission) * stable cardiovascular status (cardiac frequency \< 140 beats/min and systolic blood pressure : 90-160 mmHg without catecholamines) * midazolam \< 0,05mg/kg/h * sufentanyl \< 0,05µ/kg/h * the disorder that caused respiratory failure and prompted mechanical ventilation is treated * the clinician suspects the patient may be ready to begin the weaning process * inspiratory oxygen fraction (FiO2) \< 50% * positive end-expiratory pressure \< or equal 8cmH2O * during the day, the patient tolerate pressure support ventilation (pressure support level \< 15cmH2O * respiratory frequency (FR) \< 35 breaths/min * tidal volume (VT) \> 5ml/kg * PaO2/FiO2 \> 200 mmHg * FR/VT \< 105 breaths/min/L Exclusion Criteria: * sleep apnea, central * narcolepsy * Encephalopathy, Metabolic AND Encephalitis