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AaDO2 Calculator (Alveolar-Arterial Oxygen Gradient)
AaDO2 = PAO2 – PaO2
PAO2 = { (Pb – PH2O) x FiO2 } – ( PCO2 / R )
Pb : Barometric pressure (mmHg)
PH2O : Water vapor pressure (mmHg, 47 at 37°C)
R : Respiratory quotient, 0.8 if FiO2 < 0.9, 1.0 if > 0.9
Normal AaDO2 Range
For people in their 20s, normal AaDO2 is less than 5-10 mmHg. However, as age increases, PaO2 normally decreases, so AaDO2 may increase slightly. It's easy to think that AaDO2 increases by 3 mmHg every 10 years after age 20. Therefore, an AaDO2 of 20 in an 80-year-old patient can be considered within normal range.
Approximate calculation: Upper limit of AaDO2 by age
- 20s -- Less than 10
- 30s -- Less than 12.5
- 40s -- Less than 15
- 50s -- Less than 17.5
- 60s -- Less than 20
- 70s -- Less than 22.5
- 80s -- Less than 25
FiO2 Values by Type of Oxygen Inhalation Therapy
(1) Nasal cannula
| 100% O₂ flow rate (L/min) | FiO₂ |
|---|---|
| 1 | 0.24 |
| 2 | 0.28 |
| 3 | 0.32 |
| 4 | 0.36 |
| 5 | 0.40 |
(2) Simple mask
| 100% O₂ flow rate (L/min) | FiO₂ |
|---|---|
| 5~6 | 0.4 |
| 6~7 | 0.5 |
| 7~8 | 0.6 |
(3) Reservoir mask
| 100% O₂ flow rate (L/min) | FiO₂ |
|---|---|
| 6 | 0.6 |
| 7 | 0.7 |
| 8 | 0.8 |
| 9 | >0.8 |
| 10 | >0.8 |
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