Noninvasive ventilation in patients with persistent hypercapnia

Chronic respiratory failure is caused by insufficiency of the inspiratory muscles, i.e. mainly the diaphragm, which represents the so-called "respiratory pump". Insufficiency of the respiratory pump causes hypercapnia. Diseases with chronic hypercapnia are characterized by reduced survival. Mechanical ventilation-mostly applied as noninvasive mechanical ventilation (NIV)-improves ventilation and unloads the inspiratory muscles. Strong evidence supports the use of domiciliary NIV already in mild degrees of chronic respiratory failure caused by neuromuscular diseases, thoracic restrictions and obesity hypoventilation. In these diseases long-term NIV improves both physiological parameters (such as blood gases) and clinical outcome, e.g. exercise capacity, right heart dysfunction, sleep quality, disease-specific aspects of health-related quality of life (HRQL) and survival rate. In contrast, its influence on long-term survival in chronic obstructive pulmonary disease (COPD) patients is not clearly proven. Prescription of home NIV in COPD should therefore be restricted to severe degrees of chronic respiratory failure. Finally, there is an indication for domiciliary NIV in patients after prolonged weaning from mechanical ventilation. This paper elaborates underlying pathophysiology, diseases and how NIV works in chronic hypercapnic respiratory failure.