9. Small Group Gas Exchange

Question 1

formula for the A-a difference?

Answer 1

PA02 = PI02 –(1.2)(PaCO2)

Question 2

how does an A-a difference help assess hypoxemia?

Answer 2

normal A-a difference indicates that the lung is functioning normally, and any hypoxemia is due to decr alveolar P02 (hypovent, decr FI02, decr baromet pressure).
widened A-a difference indicates impaired gas transfer.

Question 3

in the presence of a VQ mismatch and hypoventilation, will the P02 correct itself with administration of 100% 02?

Answer 3

yes

Question 4

in the presence of a shunt, will the P02 correct itself with administration of 100% 02?

Answer 4

no – the blood does not get close enough to the alveoli for this to make any difference

Question 5

what is a normal Aa difference?

Answer 5

10-12

Question 6

if the PaCO2 is elevated, the Pa02 is low, but the A-a difference is normal, what would be an explanation?

Answer 6

hypoventilation. also high altitude, low %02 inspired.

Question 7

if the %02 in inspired air is changed, how do you calculate the new PI02?

Answer 7

PI02 = (760-47)*(%02)
Normally the %02 is 21, so PI02 is 150.
47 = water vapor pressure

Question 8

what does anemia impact: gas exchange? 02 content? delivery to tissues?

Answer 8

does not impact gas exchange. does impact 02 content and delivery to tissues. if decr Hb, arterial P02 will be normal, but 02 CONTENT will be less.