This version was machine-translated from German and has not been medically reviewed. The authoritative version is the German version.
Alveolar-arterial O₂ gradient
PAO₂ − PaO₂ from FiO₂, barometric pressure, PaCO₂ and PaO₂ – with age-dependent expected value
Calculation aid for healthcare professionals: the calculator reproduces what the sources cited assign to the inputs. Clinical assessment and every treatment decision remain with the treating physician. Inputs and results are not stored.
Frequently asked questions
Alveolar-arterial O₂ gradient: What does this calculator compute?
Calculates the alveolar-arterial oxygen gradient (A-a) using the alveolar gas equation (PAO₂ = FiO₂ × (Patm − 47) − PaCO₂/0.8) and optionally shows the approximation 2.5 + 0.21 × age (textbook approximation, not validated for children); an elevated gradient suggests impaired gas exchange, a normal gradient with hypoxaemia suggests hypoventilation.
Alveolar-arterial O₂ gradient: Which sources is this calculator based on?
Fenn WO, Rahn H, Otis AB: A theoretical study of the composition of the alveolar air at altitude (Am J Physiol 146:637–653) (1946)