This study received an unfavorable opinion from the Ethics Committee to extend the study.

The mechanical ventilation weaning must begin as early as possible to limit its complications and requires a spontaneous breathing trial (SBT) before the separation from the ventilator to the patient.

However, some patients fail this test and cannot be extubated. The main causes are pulmonary edema and diaphragmatic dysfunction. Predicting the risk of failure before carrying out the SBT makes it possible to anticipate a failure of the extubation and to adapt the therapies as well as possible. To assess the risk of pulmonary edema, cardiac preload, which corresponds to the end-diastolic filling volume of the ventricle, can be estimated using simple tests as the passive leg raising test before an SBT.

However, this test requires tilting the patient's trunk and raising the lower limbs to 45°, and is not practical, especially in intensive care.

The Müller maneuver, which allows maximum inspiratory pressure measurement via a one-way valve connected to the intubation tube, is currently used in routine care for diaphragmatic assessment. The endothoracic depression induced by this test is likely increasing venous return and cardiac output in patients with a reserve of preload, i.e. in preload-dependent patients. This test would be an easy alternative to the passive leg raising test used in current practice.

The objectif is to assess whether the presence of an independant prelaod state, as detected by the absence of increased cardiac output during the Müller maneuver, is associated with the occurence of pulmonary edema during weaning from mechanical ventilation.

The study consist in the measurement of cardiac output before and after the passive leg raising test and the Müller maneuver, then measurement of cardiac output before and after an SBT.

A transthoracic ultrasound and a blood sample with dosage of proteins and hemoglobin will be carried out initially and then at the end of the SBT as part of routine care.

The investigators hypothesize:

• The Müller maneuver induces a greater increase in cardiac output in patients in a state of preload dependancy than in patients in a state of preload independancy.
• The absence of documented preload dependancy during a Müller maneuver is associated with the occurrence of pulmonary edema during an SBT.

The investigators included patients :

• > 18 years old, conscious patient, with health insurance, placed under mechanical ventilation for at least 24 hours ;
• In whom it was decided to perform a passive leg raising test and an SBT. The investigators excluded pregnancy, patient with chest tube, particpation in another interventional study, tracheostomy, patient under legal protection.

The mechanical ventilation weaning must begin as early as possible to limit its complications and requires a spontaneous breathing trial (SBT) before the separation from the ventilator to the patient. The main causes of weaning failure are pulmonary edema and diaphragmatic dysfunction. Predicting the risk of failure before carrying out the SBT makes it possible to anticipate a failure of the extubation and to adapt the therapies as well as possible.

To predict the risk of pulmonary edema, physician could 1/ estimate the cardiac preload, which corresponds to the end-diastolic filling volume of the ventricle, using simple tests as the passive leg raising test before an SBT. This test requires tilting the patient's trunk and raising the lower limbs to 45°, and is not practical, especially in intensive care 2/ measure the hemoconcentration (hemoglobin and protein variation before and after SBT). However, this tests are not easy in intensive care unit.

The Müller maneuver, which allows maximum inspiratory pressure measurement via a one-way valve connected to the intubation tube, is currently used in routine care for diaphragmatic assessment. The endothoracic depression induced by this test is likely increasing venous return and cardiac output in patients with a reserve of preload, i.e. in preload-dependent patients. This test would be an easy alternative to the passive leg raising test used in current practice.

The objectif is to assess whether the presence of an independant prelaod state, as detected by the absence of increased cardiac output during the Müller maneuver, is associated with the occurence of pulmonary edema during weaning from mechanical ventilation. The investigators include patients:

• Placed under mechanical ventilation for at least 24 hours ;
• In whom it was decided to perform a leg lift test and an SBT. Patients are intubated and ventilated on the ventilators of the intensive care unit (v500, Dräger Medical, Lübeck, Germany or Carescape r860, GE Healthcare, Buc, France). The initial settings are decided by the physician in charge of the patient according to the gas exchanges.

The passive leg raising test consists of transferring a patient from a semi-sitting position to a position in which the trunk is horizontal and the lower limbs are elevated at 45°. This is achieved by the electrically operated bed. The test is considered positive (preload dependency) if the cardiac output increases more than 10%. This test is performed in common practice to assess the cardiac preload of patients before an SBT. The cardiac output is measured by transpulmonary thermodilution (if the patient is equiped by this dispositif before the study) or by cardiac echography.

SBT consists of reproducing the ventilation conditions once the patient has been extubated. This test is carried out using a so-called "T" piece connected to the end of the intubation tube or by canceling the assistance of the ventilator during 30 minutes. This test is performed daily in intensive care in the intubated patient before any extubation.The determination of hemoglobin and plasma proteins consists of a blood sample via a catheter already in place and its analysis before and after the SBT. An increase in hemoglobin or plasmatique proteins by 6% detect a weaning pulmonary edema .

The acts/procedures added by the search are:

• Transthoracic ultrasound added for research if the monitoring system PiCCO2 is not set up in the patient as part of the treatment. Transthoracic echocardiography is a medical imaging technique based on the use of ultrasound, inaudible, painless and harmless sound waves that allow visualization of the cardiac silhouette, its functioning and allows measurement of cardiac output, fraction ventricular ejection and other diagnostic parameters for left heart failure and pulmonary edema (E/A and E/e' ratios). This technique is used in routine daily practice by physicians in charge of patient.
• Performing a Müller maneuver after the passive leg raising test. The Müller maneuver is used in current practice for measuring the maximum inspiratory pressue before performing an SBT. It consists of using a one-way valve connected to the intubation tube allowing forced inspiration with a closed glottis, and lasts about twenty seconds.
• Measurement of cardiac output before and after a passive leg raisong, a Müller maneuver and an SBT.

Since the observation of cardiac output during the Müller maneuver is not taken into account for the management of patients suitable for research, the research will not be able to lead to a direct benefit for the participants.

On the other hand, in the event of positive results of the study, a collective benefit is expected.

Inclusion Criteria :

• Men and women over 18 years old ;
• With health insurance ;
• Placed under mechanical ventilation for at least 24 hours ;
• Conscious patient.

Exclusion Criteria:

• Pregnancy (blood assay of βHCG) ;
• Participation in another intervention study ;
• Patient with chest tube
• Tracheostomy ;
• Patient under legal protection ;
• Patient receiving state medical assistance (AME).

Experimental