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A-a Gradient

Calculate the Alveolar-arterial oxygen gradient to differentiate between pulmonary and extrapulmonary causes of hypoxemia based on ABG results.

ABG & Vitals

50 YRS
21 %
40 mmHg
90 mmHg
760 mmHg

CANVATOOLS

Pulmonology & Critical Care

A-a Gradient Report

Jul 29, 2026, 08:31 PM

ID: AAG-948011

Patient Name

John Doe

Calculated A-a Gradient

9.7

mmHg

NORMAL

Age-Adjusted Expected

~ 16.5 mmHg

Hypoventilation or low inspired PiO2 (e.g., high altitude).

ABG Parameters

FiO221%
PaCO240 mmHg
PaO290 mmHg
Calculated PAO299.7 mmHg

Calculated using Alveolar Gas Equation. Normal A-a gradient increases with age. Assumes RQ = 0.8 and body temp PH2O = 47 mmHg.

*** End of Report ***

Clinical Precision & Methodology

The Alveolar-arterial (A-a) oxygen gradient helps identify the underlying cause of hypoxemia. By comparing the calculated oxygen in the alveoli (PAO2) to the measured oxygen in the arteries (PaO2), clinicians can pinpoint respiratory shunts or diffusion defects.

Alveolar Gas Equation

Calculates PAO2 by adjusting for inspired oxygen concentration, atmospheric pressure, water vapor pressure in the lungs, and arterial carbon dioxide divided by the respiratory quotient.

Age-Adjusted Baseline

Automatically calculates the expected "normal" gradient for the patient's age. The A-a gradient naturally widens as patients age due to physiological changes in the lungs.

Thermal Receipt Export

Generates a high-resolution, perfectly scaled PNG image designed specifically for 80mm thermal printers, enabling instant clinical handouts.

Diagnostic Interpretation

Normal GradientHypoventilation (CNS depression, neuromuscular disease) or Low PiO2 (high altitude).
Elevated GradientV/Q Mismatch (PE, asthma, COPD), Right-to-Left Shunt (cardiac abnormalities), or Diffusion Defect (fibrosis).