An arterial blood gas is the ‘gold standard’ measurement because it analyses gases directly from an artery. In an acute setting, arterial blood gas samples are recommended as it gives the most accurate measurement of PaO2, although there is increasing evidence for ELCBG’s in the acute setting in a normoxic environment.

Arterial blood gas measurements do have limitations. The test is difficult to perform and can only be performed by appropriately trained staff, often these being doctors. It can also be particularly painful for the patient, which is generally why they prefer an ELCBG.