2. Gas exchange

Question 1

PA02 vs PaO2

Answer 1

A- alveoli
a- arterial blood

Question 2

explain why alveolar pO2 is lower than upper respiratory tract pO2

Answer 2

old air remains in the lung when we inspire, so only around 10% of air in lungs is ‘fresh’, and the older air has had O2 continually extracted

Question 3

henry’s law

Answer 3

solubility of a gas at a given temperature

Question 4

causes of V/Q <1

Answer 4

-asthma
-COPD early
-pneumonia
-neonatal RDS
-pulmonary oedema

Question 5

pulmonary shunt

Answer 5

smooth muscle vasoconstriction so blood is redirected away from poorly ventilated area, so no gas exchange occurs in that area and even 100% O2 can’t overcome the hypoxia

Question 6

difference between SaO2 and PaO2

Answer 6

SaO2- % of Hb bound to O2
PaO2- amount of O2 dissolved in the blood

Question 7

in anaemia, is SaO2, PaO2 and O2 content normal?

Answer 7

O2 content no, others yes

Question 8

limit for tissue pO2

Answer 8

minimum 3 kPa

Question 9

fatal level for HbCO

Answer 9

> 50%

Question 10

does CO decrease PaO2?

Answer 10

no

Question 11

what is an arterial blood gas?

Answer 11

partial pressure of oxygen in arterial blood (kPa)