L'insuffisance respiratoire aiguë du syndrome de Guillain-Barré et de la myasthénie auto-immune. De la détection au sevrage de la ventilation mécanique

Guillain-Barré syndrome (GBS) and myasthenia gravis (MG) are the most common neuromuscular causes of acute respiratory failure. Their prognosis has been considerably improved by the advent of mechanical ventilation. However patients remain at risk of respiratory arrest, because the severity of respiratory failure is often underestimated as patients often have minimal symptoms. Aspiration pneumonia, nonspecific complications of mechanical ventilation and weaning failure may also occur. Respiratory failure may be due to weakness of inspiratory and/or expiratory muscles, which can be assessed by the measurement of vital capacity (VC) and static maximal pressures. Bulbar dysfunction may also be a contributory factor. Patients with respiratory symptoms, especially orthopnoea, a reduction of VC below 60% of the predicted value or bulbar weakness must be referred to intensive care, particularly since GBS follows a progressive course and MG is characterized by fluctuating motor deficit. Criteria for mechanical ventilation include signs of respiratory distress, hypoxemia, hypercapnia or a VC below 20% predicted, but because of the risk of aspiration, major bulbar weakness can also be considered to be an indication. Weaning should only be started if there has been neurological improvement and VC is above 20%. Extubation should be preceded by a prolonged trial of spontaneous ventilation. Measurement of VC is essential at each step of the evolution of neuromuscular respiratory failure.