Difficulties to enroll patients

Exploration of the effects on diaphragmatic electrical activity (EMG) and on respiratory pattern of various level of assistance delivered by the ventilator in intubated spontaneously breathing patients in pressure support (PS) and in Neurally Adjusted Ventilatory Assist (NAVA) by step by step increasing of the level of assistance. Flow, airway pressure, transesophageal EMG signal and transcutaneous EMG signal will be recorded.

Exploration of the effects on diaphragmatic electrical activity (EMG) and on respiratory pattern of various level of assistance delivered by the ventilator in intubated spontaneously breathing patients in pressure support (PS) and in Neurally Adjusted Ventilatory Assist (NAVA) by step by step increasing of the level of assistance. Flow, airway pressure, transesophageal EMG signal and transcutaneous EMG signal will be recorded.

Aims of the study:

1. To study the electrical diaphragmatic signal variations and the ventilatory profile variations under various level of assistance (delivered by the ventilator) in PS and in NAVA in intubated spontaneously breathing patients
2. To compare a non invasive technique of diaphragmatic electrical activity recording under various levels of assistance with the invasive reference technique

Inclusion Criteria:

- Patients admitted to the ICU, intubated for acute respiratory failure, and ventilated in PS mode will be eligible for inclusion in the study.

Exclusion Criteria:

• Severe hypoxemia requiring an FIO2 > 0.5
• hemodynamic instability (defined as the need for high doses of catecholamines namely ≥ 0.5 μg/kg min- and/or high need in volume resuscitation namely more than two litres of crystalloids in two hours-)
• oesophageal problem such as hiatal hernia, oesophageal varicosities, oesophageal surgery;
• active upper gastro-intestinal bleeding;
• known coagulation disorder;
• any other contraindication to the insertion of a naso-gastric tube;
• poor short term prognosis (death expected within the next seven days)
• age < 18 years old.