A-a Gradient
Used to determine cause of hypoxemia
0.8 is a frequently used estimate
The mechanism of hypoxemia is often multifactorial, meaning that many disease-states will cause hypoxemia via a combination of V/Q mismatch, shunt, and diffusion impairment.
Common causes of V/Q mismatch include obstructive pulmonary disease, interstitial lung disease, and pulmonary vascular disease.
Common causes of shunt include arteriovenous malformations, hepatopulmonary syndrome, and underventilated alveoli (ie. atelectasis or alveoli filled with edema, pus, blood, etc).
Common causes of diffusion impairment include interstitial lung disease and other causes of pulmonary fibrosis / inflammation.
The A-a gradient normally will increase with increasing FiO2, sometimes reaching values over 100 with inhalation of 100% oxygen. Another formula takes into account patient temperature which can have a minor impact on pH2O.
- [1]Mellemgaard, K.: The alveolar-arterial oxygen difference: its size and components in normal man.Acta Physiologica Scandinavica 1966, 67 (1): 10-20
- [2]
Results
Real-time automated computation
The mechanism of hypoxemia is often multifactorial, meaning that many disease-states will cause hypoxemia via a combination of V/Q mismatch, shunt, and diffusion impairment.
Common causes of V/Q mismatch include obstructive pulmonary disease, interstitial lung disease, and pulmonary vascular disease.
Common causes of shunt include arteriovenous malformations, hepatopulmonary syndrome, and underventilated alveoli (ie. atelectasis or alveoli filled with edema, pus, blood, etc).
Common causes of diffusion impairment include interstitial lung disease and other causes of pulmonary fibrosis / inflammation.
The A-a gradient normally will increase with increasing FiO2, sometimes reaching values over 100 with inhalation of 100% oxygen. Another formula takes into account patient temperature which can have a minor impact on pH2O.
- [1]Mellemgaard, K.: The alveolar-arterial oxygen difference: its size and components in normal man.Acta Physiologica Scandinavica 1966, 67 (1): 10-20
- [2]