Hypercapnia Effects on Lung Function.

The biological effects of hypercapnia on the lungs have been controversial. Earlier publications suggesting that hypercapnia was beneficial for mechanically ventilated patients with acute lung injury led to the clinical paradigm of "permissive hypercapnia". However, more recent studies have challenged this paradigm by reporting that hypercapnia activates signaling pathways with deleterious effects. This review focuses on the effects of elevated CO2 as a signaling molecule, highlighting the pathways and processes contributing to the detrimental effects of hypercapnia on the alveolar epithelium, the airways and immune system.