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.