A-a O2 Gradient
Enter FiO2 as a fraction from 0 to 1. Room air is 0.21.
fraction
Measured arterial oxygen partial pressure from an arterial blood gas, in mmHg.
mmHg
Measured arterial carbon dioxide partial pressure from an arterial blood gas, in mmHg.
mmHg
Use 760 mmHg at sea level unless the local barometric pressure is known.
mmHg
Routine adult bedside use commonly assumes 47 mmHg for fully humidified gas at 37 C.
mmHg
Routine bedside calculations commonly use 0.8.
ratio
Adult age in years for the expected A-a gradient reference.
years
Clinical noticeEducational use only. Interpret the A-a gradient alongside the full arterial blood gas, the actual inspired oxygen source, and the clinical context.
Context and use
Ecuación: PAO₂ = FiO₂ × (Patm - PH₂O) - (PaCO₂ / RQ)
A-a gradient = PAO2 - PaO2
Expected adult A-a gradient = (age + 10) / 4
The expected reference applies to adults and is mainly room-air-oriented.
