Interactive A-a O₂ Gradient calculator. Requires the calculator gadget.
Usage: {{Aa Gradient Calculator}}
A-a O₂ Gradient
Alveolar-arterial (A-a) O₂ Gradient
| Parameter
|
Value
|
| Age (years)
|
|
| FiO₂ (%)
|
|
| PaCO₂ (mmHg)
|
|
| PaO₂ (mmHg)
|
|
| A-a Gradient
|
mmHg
|
| Expected A-a
|
mmHg (age-adjusted normal)
|
Interpretation
- Normal A-a gradient ≈ (Age/4) + 4 on room air
- Elevated A-a gradient suggests: V/Q mismatch, shunt, or diffusion impairment
- Normal A-a gradient + hypoxia suggests: hypoventilation or low FiO₂
|
References
- Formula: A-a = [FiO₂ × (Patm – PH2O)] – (PaCO₂/0.8) – PaO₂
- Kanber GJ, et al. The alveolar-arterial oxygen gradient in young and elderly men during air and oxygen breathing. Am Rev Respir Dis. 1968;97(3):376-381. PMID 5637791.
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