Critical illness neuromyopathy is a common disease acquired during ICU stay leading to a deep weakness involving the respiratory muscle work which result in a delayed weaning of mechanical ventilation.

The main objective is to quantify the loss of diaphragm function by measuring the diaphragm force (using the non invasive method by phrenic nerve stimulation allowing to measure the twitch airway pressure during airway occlusion) in a selected population of patients with critical illness neuromyopathy (defined as a MRC score < 48).

The second end points are to evaluate its incidence, the consequences on the patients outcome (extubation success or failure; ICU stay) and to evaluate the relations between diaphragm function (twitch airway pressure during airway occlusion, maximal inspiratory pressure and diaphragm thickness evaluated by ultrasound) and peripheral limbs force (evaluated by the Medical Research Council - MRC score).

Diaphragm function will be assessed through phrenic nerve stimulation allowing to measure the twitch airway pressure during airway occlusion (expressed in cmH2O). It will be assessed during a spontaneous breathing trial for each patient with a known critical illness neuromyopathy. The diaphragm (thickness and course) will be studied by ultrasound assessment as well. Peripheral limbs force will be evaluated by the MRC score. A total of 40 analysable patients will be included.

All these measurements will be made at the time of the spontaneous breathing trial (SBT) during the weaning phase. No modification of the clinical practices of the care should be modified by the study. The twitch airway pressure during airway occlusion will be assessed at the begining of the SBT. The other measurements will be performed 30 mn after the SBT if this one will be well tolerated.

Participants will be followed for the duration of ICU stay.

Inclusion Criteria:

• MRC score <48
• ready for weaning from mechanical ventilation

Exclusion Criteria:

• previous history of neuromyopathy
• impossibility to perform a magnetic stimulation
• cervical spine injury
• bihemispheric or brain stem lesion

patients acquired weakness and neuromyopathy in ICU