Clinical use
Use this calculator for alveolar-arterial oxygen gradient in thepulmonary workflow. It is decision support and should be interpreted with the patient context, local protocols, and clinician judgment.
Calculate A-a
Interpretation
Expected A-a gradient = (Age/4) + 4. Elevated gradient suggests V/Q mismatch, shunt, or diffusion impairment. Normal gradient with hypoxemia → hypoventilation.
Required inputs
- Pao 2
- Paco 2
- Fio 2
- Age
Optional: Atmospheric Pressure
Evidence and limitations
This page cites 1 published reference. Confirm units and inclusion criteria before applying the output; calculators do not replace assessment, escalation, or local policy.
References
- Kanber GJ et al. JAMA 1968;203:281-284
Frequently asked questions
What is the A-a Gradient?
A-a Gradient is a clinical calculator used for Alveolar-arterial oxygen gradient.
How do I interpret the A-a Gradient?
Expected A-a gradient = (Age/4) + 4. Elevated gradient suggests V/Q mismatch, shunt, or diffusion impairment. Normal gradient with hypoxemia → hypoventilation.
What inputs are required for the A-a Gradient?
Required inputs include Pao 2, Paco 2, Fio 2, Age. Optional inputs include Atmospheric Pressure.
What is the evidence behind the A-a Gradient?
The A-a Gradient page cites Kanber GJ et al. JAMA 1968;203:281-284.
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Next steps
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