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

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  1. See Also
    1. Arterial Blood Gas
  2. Physiology
    1. Efficiency of gas exchange between alveolus and artery
  3. Calculation at sea level
    1. A-a gradient = PaO2 - FIO2 x (760 - 47) - (PaCO2/0.8)
    2. FIO2 on room air = 0.21
  4. 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
  5. Increased A-a gradient
    1. Pulmonary Embolism

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