A-a gradient
Medical abbreviation · Respiratory
| Stands for | Alveolar-arterial oxygen gradient |
|---|---|
| Categories | Medical |
A-a gradient stands for Alveolar-arterial oxygen gradient, a respiratory abbreviation.
Difference between the oxygen pressure in the air sacs, calculated with the alveolar gas equation, and in arterial blood measured by a blood gas. It indicates whether low blood oxygen is due to lung disease or to underbreathing.
Example: PaO2 58 with A-a gradient 42 on room air: points to V/Q mismatch, likely PE or pneumonia.
Usage notes
A normal gradient is roughly the patient's age divided by 4, plus 4, on room air. Hypoxemia with a normal gradient suggests hypoventilation (for example opioid overdose) or high altitude, whereas a raised gradient indicates ventilation-perfusion mismatch, shunt or diffusion problems. The gradient widens on supplemental oxygen, so it is most useful on room air.
Related abbreviations
More respiratory abbreviations
- AATD – Alpha-1 antitrypsin deficiency
- ABPA – Allergic bronchopulmonary aspergillosis
- AC – Assist-control ventilation
- AECOPD – Acute exacerbation of chronic obstructive pulmonary disease
- AERD – Aspirin-exacerbated respiratory disease
- AHI – Apnea-hypopnea index
- AHRF – Acute hypoxemic respiratory failure
- APAP – Automatic positive airway pressure
- APRV – Airway pressure release ventilation
- ARDS – Acute respiratory distress syndrome
- ARF – Acute respiratory failure
- ATS – American Thoracic Society
See all 109 respiratory abbreviations →
This entry is for general education and is not medical advice. Abbreviation use varies between institutions; always confirm in context.