How to calculate Alveolar Arterial Oxygen Gradient
A-a Oxygen Gradient = PAO2 – PaO2
PAO2 = ( FiO2 * (760 – 47)) – (PaCO2 / RQ)
PaO2 = Arterial PO2 (measured in arterial blood)
A-a Oxygen Gradient (expanded form) = (FiO2 * (Patm – PH20) ) – (PaCO2/RQ) – PaO2
What is the normal A-a Gradient
A normal A–a gradient for a young adult is between 5–10 mmHg. A–a gradient increases with age. For every decade a person has lived their expected A–a gradient typically increases by 1 mmHg. Furthermore a higher A-a gradients is associated with oxygen transfer / gas exchange problems.
Hypoxemia is a below normal level of oxygen in your blood. Moreover hypoxemia is a sign of a variety of problems related to breathing or circulation, and may result in various symptoms, such as shortness of breath.
- Right-to-left shunt
- V/Q mismatch
- Diffusion impairment
- Low inspired O2