Pathology - Hypoxemia

Question 1

What is normal PaO2?

Answer 1

10.5 - 13.5 kPa

Question 2

What is normal PaCO2 range?

Answer 2

4.8 - 6 kPa

Question 3

What is type 1 respiratory failure?

Answer 3

PaO2 <8 kPa

PaCO2 can be normal or low

Question 4

What is type 2 respiratory failure?

Answer 4

PaCO2 > 6.5 kPa - inability to remove CO2 effectively

PaO2 is also usually low

Question 5

What is hypoxaemia and what 4 states are normally associated with it?

Answer 5

An abnormally low level of PaO2

Ventilation/Perfusion (V/Q) mismatch

Alveolar hypoventilation

Shunt

Diffusion impairment

Question 6

Why does COPD cause hypoxaemia?

Answer 6

Has all 4 states

V/Q mismatch - caused by AFO

Alveolar hypo-ventilation - caused by a reduced respiratory drive

Diffusion impairment - due to loos of alveolar SA

Shunt - only in acute infective exacerbation of COPD

Question 7

Why does Pneumonia cause hypoxaemia?

Answer 7

V/Q mismatch - bronchitis/bronchopneumonia

Shunt - severe broncho-pneumonia OR in lobar pattern pnemonia with areas of consolodation

Question 8

What is V/Q mismatch? How to treat it?

Answer 8

A normal breath in is 4L/min, CO is 5l/min
V/Q should be 0.8

A low V/Q is commonest cause of hypoxaemia

Responds well to increasing FiO2 - fraction of inspired O2

Question 9

What is a shunt? How does it respond to increasing FiO2?

Answer 9

Blood passing from RA to RV past alveoli and not being ventilated

Large shunts respond poorly to increasing FiO2 as blood

Question 10

What is alveolar hypoventilation? How is it corrected?

Answer 10

Amount of air moving in and out of lungs is affected

PACO2 increases which increases PaCO2

PAO2 deacreases which causes PaO2 to also fall

Fall in PaO2 corrected via increasing FiO2

Question 11

What pulmonary vasculature changes occur in hypoxia?

What about hypoxaemia?

Answer 11

Pulmonary arterioles constrict when PAO2 falls in a local area to redirect blood to a well ventilated area

In hypoxaemia ALL vessels restrict

Question 12

What is Cor Pulmonale?

Answer 12

Hypertrophy of RV resulting from a disease affecting the function/structure of lung making right side of heart work harder

Question 13

What causes cor pulmonale in hypoxia?

Answer 13

Pulmonary vessels constrict

Pulmonary arterioles go through hypertrophy and intima layer fibrosis

Loss of capillary bed

All this makes right side of heart work harder