In case of respiratory distress, patients are intubated to be connected to an artificial respirator to ensure gas exchanges. Before any ventilatory weaning, a breathing test in spontaneous ventilation under artificial nose is practiced. The patient keeps the endotracheal tube but is no longer assisted by the ventilator. Mortality is markedly increased with the prolongation of the weaning period. Despite the presence of all weaning criteria and the success of a breathing test in spontaneous ventilation under artificial nose, failure of extubation occurs in 20% of patients.