ABSTRACT
The term respiratory failure describes a condition in which the respiratory system fails in one or both of its principal gas exchange functions: oxygenation and elimination of carbon dioxide. In clinical practice it is conventionally defined as an arterial oxygen tension (PaO2) <60 mmHg, an arterial carbon dioxide tension (PaCO2) >45 mmHg, or both, while breathing air. It is important to emphasize that respiratory failure is a laboratory diagnosis and that there is no absolute definition of the levels of arterial PaO2 and PaCO2 that indicate respiratory failure: the cutoff levels serve as a general guide, and their significance depends on the history and clinical assessment of patients.
