Principles of Gas Exchange

Question 1

oxygenation

Answer 1

Process of delivering oxygen from the alveoli to the tissues

Question 2

ventilation

Answer 2

Delivers oxygen rich air to the alveoli

Question 3

What is the RLS for oxygenation?

Answer 3

rate of diffusion across the alveolar membrane

Question 4

What is the RLS for ventilation ?

Answer 4

air movement

lung mechanics matter more than diffusion

Question 5

oxygen carrying capacity

Answer 5

how much oxygen is carried

Hb carries >100x more oxygen than is dissolved in the blood

Question 6

What affects oxygen carrying capacity?

Answer 6

PaO2

if pressure is higher, hemoglobin will be more saturated

Question 7

Oxygen delivery

Answer 7

DO2

dependent on cardiac output

normally drop off 25% of O2 in normal capillaries

Question 8

What is oxygenation dependent upon?

Answer 8

diffusion of oxygen across alveolus

hemoglobin to supply oxygen carrying capacity

cardiac output to deliver oxygen to tissues

Question 9

Leftward shift on O2 dissociation curve

Answer 9

increased affinity for oxygen

Question 10

Rightward shift on O2 dissociation curve

Answer 10

decreased affinity for oxygen

Question 11

What is normal PaO2 in the capillaries?

Answer 11

40 mg

Question 12

What is normal O2 sat in the capillaries?

Answer 12

75%

Question 13

What drives oxygenation diffusion from alveolus to capillaries?

Answer 13

driven by gradient between PA (atmosphere?) and Pa (alveolus)

PAO2 = 100 mg
PaO2 = 40 mg

Question 14

Why does CO2 gradient not change much?

Answer 14

due to association with pH, which is tightly regulated

Question 15

How can you impair O2 diffusion?

Answer 15

decrease PAO2 (less gradient)

increased interstitial fluid in alveolus

Question 16

How can you tell there is a problem with ventilation?

Answer 16

labored breathing

Question 17

Why do we start to give oxygen at 90% O2 sat

Answer 17

you are at a PaO2 of 60 which means you already lost 40% of carrying capacity

you’re also close to the “steep” part of the curve

Question 18

limitations of pulse ox

Answer 18

multiple variables define O2 carrying capacity

not reliable with decreased perfusion

Question 19

pulse oximetry

Answer 19

measures O2 sat by using light absorbance

oxygenated Hb absorbs light at 940 mm

deoxygenated Hb absorbs light at 660 mm