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A-a GradientAka: Alveolar-Arterial Oxygen Tension Difference, PO2 difference, DO2

See Also
1. Arterial Blood Gas
Physiology
1. Efficiency of gas exchange between alveolus and artery
Calculation at sea level
1. A-a gradient = PaO2 - FIO2 x (760 - 47) - (PaCO2/0.8)
2. FIO2 on room air = 0.21
Normal A-a gradient
1. A-a gradient = (Age/4) + 4
2. Young person at sea level
  1. A-a increases 5 to 7 mmHg for every 10% increase FIO2
  2. Room Air: 10 to 20 mmHg
  3. 100% oxygen: 60 to 70 mmHg
3. Increased age affects A-a gradient (at sea level)
  1. Age 20 years: 4 to 17 mmHg
  2. Age 40 years: 10 to 24 mmHg
  3. Age 60 years: 17 to 31 mmHg
  4. Age 80 years: 25 to 38 mmHg
Increased A-a gradient
1. Pulmonary Embolism

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 8/14/2009. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.