The synchronization between the patient and the ventilator is an essential objective during mechanical ventilation (MV). Maintaining the patient's respiratory activity during MV reduces ventilation pressures, improves oxygenation, and decreases sedation. In order to do this, the inspiratory or expiratory effort of the patient must be detected by the respirator' sensor systems, so that the assistance delivered by the respirator is coordinated with the patient's respiratory cycles. The usual systems do not actually detect the beginning of the effort but its result: variation in flow rate or pressure at the respirator circuit, which depends on the patient's respiratory mechanics and sensitivity of the sensor. This detection is currently imperfect, which generates asynchrony between the patient's needs and the assistance of the respirator. The asynchrony comprises the periods of delay between the beginning of the inspiration (or expiration) and the response of the respirator, but also of the unsuitable cycles: inspiratory efforts of the patient not detected by the respirator, or inversely triggering assistance in the absence of inspiration by the patient (self-initiation), or delivery of 2 cycles of assistance for a single inspiration (double triggering).

Asynchrony is a risk factor for prolonged mechanical ventilation in adults. Adult studies have shown that patient-ventilator asynchrony is common during MV, and is associated with prolonged MV duration. An association with length of stay in intensive care and in hospital was also observed. In children, patient-ventilator synchronization is more difficult to achieve than in adults due to a higher respiratory rate and smaller current volumes. The impact of patient-ventilator asynchrony on evolution has not been studied in pediatrics.

Patient-ventilator synchronization could be improved by the development of new ventilatory modes. The new NAVA (neurally adjusted ventilatory assist) ventilation mode detects the patient's breathing efforts earlier by monitoring the electrical activity of the diaphragm through the esophagus. This new mode seems to improve synchronization in children. NAVA ventilation may therefore be a step forward, but its clinical benefits remain to be seen.

The objective of this study is to evaluate the impact of patient-ventilator asynchrony on the duration of mechanical ventilation in children with acute respiratory failure.

Inclusion Criteria:

• Mechanical ventilation planned for more than 24h according to the physician in charge;
• Presence of a spontaneous respiratory activity (defined by the presence of respiratory cycles activated by the patient);
• Parental consent obtained with the parents or with the legal representative.

Exclusion Criteria:

• pathologies for which a long and difficult weaning of the mechanical ventilation is expected: chronic respiratory failure with history of ventilation superior to one month, severe neurological or muscular pathology;
• Patients with a tracheotomy;
• Patients receiving a treatment by curare;
• Contraindication of recording of the diaphragmatic activity by oesophageal way, in particular recent oesophageal surgery, oesophageal stenosis, suspicion of diaphragmatic paralysis, severe coagulation disorder;
• Patients to whom a death seems imminent;
• Patients for whom a limitation of the care was considered.

Patients under mechanical ventilation for acute respiratory failure