Hypoxemia algorithm

Question 1

How would you calculate the Aa gradient
What is the normal Aa gradient
-how would you adjust for age

Answer 1

PAO2 - PaO2
PAO2 = (FiO2 x (Pb- PH2O)) - (PaCO2/R)

1.33-2kPa but increases with age
(age/4) +4

Question 2

How would you interpret a normal Aa gradient

Answer 2

(age/4) + 4

-hypoxemia due to hypoventilation or altitude

Question 3

How would you interpret an increased Aa gradient

What would you do

Answer 3

Problem with the alveolar capillary exchange surface

FiO2 100%

• responsive => due to low V/Q
• decreased response => due to a shunt