Which of the following is/are true regarding the PACO2?

1. Directly proportional to whole-body carbon dioxide production
2. Directly proportional to alveolar ventilation (VA)
3. Normally maintained at approximately 35 to 45 mm Hg
a. 2 and 3 only
b. 3 only
c. 1 and 2 only
d. 1 and 3 only

ANS: D
PACO2 varies directly with the body's production of carbon dioxide (CO2) and inversely with alveolar ventilation (VA). Under normal conditions it is maintained at approximately 35 to 45 mm Hg.