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Chronic respiratory failure

Chronic respiratory failure describes a clinical state when the arterial Po2 breathing air is less than 8.0 kPa, which may or may not be associated with hypercapnia (defined as Pco2 more than 6.0 kPa (45 mm Hg)). Four processes cause arterial hypoxaemia due to inefficient pulmonary gas exchange—ventilation–perfusion (V/Q) mismatch, hypoventilation, diffusion limitation, and true shunt, with the most important of these being V/Q mismatching. The arterial CO2 is increased by inadequate alveolar ventilation and/or V/Q abnormality. A wide range of disorders can cause chronic respiratory failure, with the commonest being chronic obstructive pulmonary disease, interstitial lung diseases, chest wall and neuromuscular diseases, and morbid obesity.