The alveolar-arterial oxygen difference is an index of gas exchange within the lungs and can be used to assess the normality of blood oxygenation..
alveolar-arterial oxygen tension difference =
= (alveolar oxygen tension) - (pO2)
Interpretation:
• For FIO2 of 21%, the normal alveolar-arterial oxygen tension difference is 5-25 mm Hg; for FIO2 of 100%, the normal alveolar-arterial oxygen tension difference is < 150 mm Hg
• The alveolar-arterial oxygen difference varies with age, increasing after age 40.
• The alveolar-arterial oxygen difference is useful in distinguishing normal from mild or moderately abnormal gas exchange.
• The alveolar-arterial oxygen difference increases in most patients with abnormal gas exchange during exercise testing.
Limitations:
• In severe COPD with abnormal gas exchange, the alveolar-arterial oxygen difference may underestimate the severity of the gas exchange abnormality.
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