Alveolar: arterial (A:a) gradient
June 3, 2026
by
TCAR Education Programs, Stephen Von Weller
A measurement of the difference between oxygen concentration in the alveoli and in the arterial system. A:a gradient measurement is useful for identifying the cause of hypoxemia. The PaO2:FiO2 (P:F) ratio is the most widely used method to calculate the A:a gradient and quantify diffusion problems. The P:F ratio is calculated by dividing PaO2 by FiO2. PRONUNCIATION: al-ve-OL-ar