A-a gradient
Pronunciation: A-a gradient
The alveolar-arterial oxygen gradient, measuring the difference between alveolar and arterial oxygen partial pressures.
Full Definition
The alveolar-arterial oxygen gradient (A-a gradient) is a calculated value that represents the difference between the partial pressure of oxygen in the alveoli and in arterial blood. It is used to assess gas exchange efficiency and identify underlying lung pathology. Normal values are typically less than 10-15 mmHg in young healthy individuals, but increase with age. An elevated A-a gradient indicates impaired oxygen transfer across the alveolar-capillary membrane, which can occur in conditions such as pneumonia, pulmonary embolism, or acute lung injury.
Usage
Usage note: Always hyphenate and use lowercase 'a' for both components when writing the abbreviated form.
In Context
- "The patient's elevated A-a gradient of 45 mmHg suggested significant ventilation-perfusion mismatch." — Clinical assessment report
- "Calculate the A-a gradient using the alveolar gas equation before adjusting ventilator settings." — Treatment protocol