Hypercapnia: a nonpermissive environment for the lung

Am J Respir Cell Mol Biol. 2012 Apr;46(4):417-21. doi: 10.1165/rcmb.2011-0395PS. Epub 2012 Jan 12.


Patients with severe acute and chronic lung diseases develop derangements in gas exchange that may result in increased levels of CO(2) (hypercapnia), the effects of which on human health are incompletely understood. It has been proposed that hypercapnia may have beneficial effects in patients with acute lung injury, and the concepts of "permissive" and even "therapeutic" hypercapnia have emerged. However, recent work suggests that CO(2) can act as a signaling molecule via pH-independent mechanisms, resulting in deleterious effects in the lung. Here we review recent research on how elevated CO(2) is sensed by cells in the lung and the potential harmful effects of hypercapnia on epithelial and endothelial barrier, lung edema clearance, innate immunity, and host defense. In view of these findings, we raise concerns about the potentially deleterious effects hypercapnia may have in patients with acute and chronic lung diseases.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Acute Lung Injury / metabolism*
  • Carbon Dioxide / blood*
  • Cell Membrane / metabolism
  • Humans
  • Hypercapnia / etiology*
  • Immunity, Innate
  • Lung
  • Pulmonary Alveoli / cytology
  • Pulmonary Alveoli / metabolism
  • Pulmonary Edema / etiology
  • Respiration, Artificial


  • Carbon Dioxide