This is a multicenter, prospective, randomized, open-label study which compared two ventilation modes: spontaneous NAVA mode and spontaneous breathing with IPS mode (the latter is considered as the reference ventilatory mode) in patients admitted to the ICU for acute respiratory failure and ventilated with an endotracheal tube. NAVA mode allows to minimize patient-ventilator disharmony with acceptable tolerance and to preserve spontaneous ventilation.