Non-invasive mechanical ventilation (NIMV) is defined as the respiratory support without endotracheal intubation. Indication for mechanical ventilation is the reversible respiratory insufficiency. Respiratory insufficiency may be due to ineffective ventilation or oxygenation. Ventilation disorder may be caused by different patologies and it resolves by mechanical ventilation. Oxygenation disorder arises from the lung diseases. Non-invasive mechanical ventilators are classified as; non-invasive negative pressure ventilators and noninvasive positif pressure ventilators. NIMV is a choice when an invasive surgical procedure is needed under general anaesthesia or deep sedation, in patient with Duchenne muscular distrophy, amyotrophic lateral sclerosis, conjestif heart failure, obstructif sleep apnea syndrome.