### A-a Gradient

Barometric pressure = 760

FIO2 = .21 (room air)

Water vapor pressure at body temp = 47

Correction for respiratory quotient = 30*1.2 = 36

The formula for calculation of A-a gradient is:

**((760-47)*0.21) - 36 =114 A = 114 a = 80 A-a gradient =
34 mm Hgb**

The normal A-a gradient is below 20 mm of Hgb. Our patient has a widened A-a
gradient.