Hypercapnia in COPD: Causes, Consequences, and Therapy

Abstract

Chronic obstructive pulmonary disease (COPD) is a progressive respiratory disorder that may lead to gas exchange abnormalities, including hypercapnia. Chronic hypercapnia is an independent risk factor of mortality in COPD, leading to epithelial dysfunction and impaired lung immunity. Moreover, chronic hypercapnia affects the cardiovascular physiology, increases the risk of cardiovascular morbidity and mortality, and promotes muscle wasting and musculoskeletal abnormalities. Noninvasive ventilation is a widely used technique to remove carbon dioxide, and several studies have investigated its role in COPD. In the present review, we aim to summarize the causes and effects of chronic hypercapnia in COPD. Furthermore, we discuss the use of domiciliary noninvasive ventilation as a treatment option for hypercapnia while highlighting the controversies within the evidence. Finally, we provide some insightful clinical recommendations and draw attention to possible future research areas.

Keywords: airway immunity; chronic obstructive pulmonary disease; hypercapnia; noninvasive ventilation.

Figure 1

Diaphragmatic length–tension curve in subjects without (solid line) and with (dashed line) emphysema. In emphysema, the curve is shifted towards the left, thus shifting to shorter length.

Figure 2

Mechanisms leading to hypercapnia in stable (upper panel) and exacerbated (lower panel) COPD. V/Q: ventilation/perfusion of the alveoli. References are listed in the text.

Figure 3

Possible cellular effects of hypercapnia in COPD. Red arrows indicate a harmful effect, while black arrows show that current evidence is inconclusive. References are listed in the text.