Davis's Lab & Diagnostic Tests

Alveolar/Arterial Gradient and Arterial/Alveolar Oxygen Ratio

Alveolar/Arterial Gradient and Arterial/Alveolar Oxygen Ratio is a topic covered in the Davis's Lab & Diagnostic Tests.

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Alveolar-arterial difference, A/a gradient, a/A ratio.

Common Use:
To assist in assessing oxygen delivery and diagnosing causes of hypoxemia such as pulmonary edema, acute respiratory distress syndrome, and pulmonary fibrosis.

Arterial blood collected in a heparinized syringe. Specimen should be transported tightly capped and in an ice slurry.

Normal Findings:
(Method: Selective electrodes that measure Po2 and Pco2)

Alveolar/arterial gradientLess than 10 mm Hg at rest (room air)
20–30 mm Hg at maximum exercise activity (room air)
Arterial/alveolar oxygen ratioGreater than 0.75 (75%)

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