The Alveolar Gas Equation (PK4)

Question 1

Why is PaCO2 a clinical measure of adequacy of V̇A?

Answer 1

• V̇A is changed when V̇CO2 increases to maintain constant PACO2 (eg. in exercise)
• Therefore if PACO2 increases (thus PaCO2 too), the change in V̇A was inadequate

Question 2

Alveolar gas equation

Answer 2

PAO2 = PIO2 - (PACO2 / R)

Question 3

What value is R in the alveolar gas equation normally, and when would it change?

Answer 3

• 0.8
• Unusual diet