High Flow During Weaning From Mechanical Ventilation

Detection and relief of dyspnea in mechanically ventilated patients is a priority. Optimization of mechanical ventilation settings is unfortunately often insufficient to relieve dyspnea in patients entering the weaning process. Pharmacological treatments are effective but their use is likely to delay separation with the ventilator. Promoting the development of non-pharmacological interventions is therefore an interesting avenue. The hypothesis is that the application of high-flow humidified nasal air in orotracheally intubated patients can decrease the work of breathing and relieve dyspnea at the time of weaning from mechanical ventilation. Patients will be exposed to stepwise increase in high flow nasal air (0 L/min, 30 L/min, 50 L/min and 70 L/min) before to undergo a 60 minutes spontaneous breathing trial. During the protocol, dyspnea, inspiratory effort, respiratory drive, respiratory muscles electromyogram (EMG) and patient's comfort will be assessed.

Patients equipped with an esophageal probe and deemed ready to undergo a spontaneous breathing trial will be included.

During, the inclusion visit, main characteristics of the patients and ICU stay will be collected in the patient's chart: age, sex, comorbidities, date of admission to intensive care, date of intubation, severity score (SOFA), reason for admission to intensive care , weight, height, ventilation settings, P0.1, respiratory rate, SpO2, dyspnea and comfort score.

Secondarily, the quality of the esophageal pressure signal will be checked. Esophageal pressure will be collected using a nasogastric tube (NutriventTM, SIDAM, Italy). Esophageal pressure will be measured continuously by the Labchart system installed on the department's dedicated computer.

Third, the EMG collection device will be implemented. EMG signals will be collected by surface electrodes on the scalene and intercostal muscles and on the sides of the nose. The electrodes are connected to collection modules operating with the LabChart system.

Finally, the high-flow humidified air device will be installed (AIRVO 2; Fisher and Paykel Healthcare, Auckland, New Zealand) and nasal cannulas adapted to the patient's anatomy will be positioned. The FiO2 will be fixed at 21% for the duration of the study. The flow will be set at 0 L/min at the inclusion visit. The humidified air temperature will be set to 37°C.

The protocol will consist of installing the high-flow humidified nasal oxygen therapy device and varying the nasal flow (4 different conditions: 0 L/min, 30 L/min, 50 L/min and 70 L/min) then performing the spontaneous breathing trial (duration 60 minutes). During each of the steps of the protocol, a collection of the intensity of the dyspnea, a measurement of the esophageal pressure, a measurement of the respiratory drive, an EMG measurement of the respiratory muscles and a comfort assessment will be carried out.

Eligibility Criteria:
Inclusion Criteria:

1. Age \> 18 years old
2. orotracheal intubation
3. Decision to initiate a spontaneous breathing trial by the clinical team
4. Visual analogic scale of dyspnea \> 3/10
5. Informed consent to participate
6. Patient covered by the national health

Exclusion Criteria:

1. No esophageal probe in place
2. Extubation planned without a spontaneous breathing trial
3. Glasgow coma scale\< 12
4. Patient's refusal
5. No coverage by the national health insurance
6. Patient under legal protection of justice