Mechanical ventilation is a cornerstone in the management of severe forms of pneumonia, acute respiratory distress syndrome. It provides essential oxygen to patients, ventilates the lungs but also has deleterious effects like any treatment, in particular by reducing cardiac output by reducing venous return. Mechanical ventilation also has effects on the diaphragm: diaphragmatic dysfunction. It is explained by a prolonged inactivity of this muscle with a reduction of muscle fibers that can settle down quickly, after only a few days of mechanical ventilation. This dysfunction results in a reduction in the latter's ability to generate intrathoracic pressure necessary for ventilation, slows the withdrawal of mechanical ventilation and lengthens the duration of stay in intensive care unit. To reduce this dysfunction, phrenic stimulation has been proposed as an alternative to remuscler the diaphragm thanks to electrodes located on a central venous catheter, also used to deliver the usual therapies in intensive care unit.

The HEMOSTIM study is interested in the effects of phrenic stimulation on regional ventilation, cardiac output and cerebral perfusion: investigator hypothesize that diaphragmatic stimulation allows an improvement of these parameters.

Inclusion Criteria:

• Patient included in RESCUE 3 study, interventional arm with phrenic stimulation
• Patient or family consent

Exclusion Criteria:

• Patient not affiliated or not benefiting from a social security scheme