Small Group 2 Gas Diffusion

Question 1

How do you calculate the A-a gradient?

Answer 1

1. Calculate the pressure of inspired O2

2. Use PIO2 along with PACO2 and PaO2 to calculate A-a gradient

Question 2

What is the cause of hypoxemia most commonly in the case of lung fibrosis?

Answer 2

V/Q mismatch due to destruction of both capillaries and alveoli

Question 3

High ventilation rates can compensate for low V/Q ratio units for _____ but not _______

Answer 3

CO2 but not O2

Question 4

How does alkalosis cause the oxyhemoglobin curve to shift?

Answer 4

to the left (greater Hgb-O2 affinity which is good for pick up but does not help for off-loading in the tissues)

Question 5

What’s a good rule of thumb that helps to estimate the contribution of alveolar hypoventilation to hypoxemia?

Answer 5

alveolar hypoventilation is approximated by the excess of PaCO2 over 40mm Hg

Question 6

100% oxygen is a very sensitive way of measuring ____ ____.

Answer 6

anatomic shunts, a small decrease in O2 content due to a true stung causes a large decrease in PaO2 that is easily measured

Question 7

How can you rule out an anatomic shunt?

Answer 7

PaO2 at or greater than 550 on 100% can rule out a shunt, note if PaO2 is less than 550, that does not identify a shunt with certainty