Question: how do you calculate aa gradient?
Answer: A-a Gradient = (Age/4) + 4. Young person at sea level. A-a increases 5 to 7 mmHg for every 10% increase FIO2. Room Air: 10 to 20 mmHg. 100% oxygen: 60 to 70 mmHg. Increased age affects A-a Gradient (at sea level) Age 20 years: 4 to 17 mmHg. Age 40 years: 10 to 24 mmHg.