Arterial Blood Gases

Question 1

What are the 4 causes of low PaO2?

Answer 1

Hypoventilation
Diffusion impairment
Shunt
V/Q mismatch

Question 2

What will happen to pH, PaCO2 and [HCO3-] in metabolic acidosis?

Answer 2

pH decreased
paco2 decreased
hco3 decreased

Question 3

What will happen to pH, PaCO2 and [HCO3-] in metabolic alkalosis?

Answer 3

pH increased
paco2 increased
hco3- increased

Question 4

What will happen to pH, PaCO2 and [HCO3-] in respiratory acidosis?

Answer 4

pH decreased
pac02 increased
hco3- decreased

Question 5

What will happen to pH, PaCO2 and [HCO3-] in respiratory alkalosis?

Answer 5

pH increased
paco2 decreased
hco3- decreased

Question 6

Causes of respiratory acidosis

Answer 6

Hypoventilation eg neuromuscular diseases

Alveolar hypoventilation eg COPD

Question 7

What is the A-a gradient useful for?

Answer 7

To work out if there is a respiratory problem
A = alveolar
a = arterial

Question 8

What A-a gradient suggests lung pathology?

Answer 8

> 4kPa

In healthy, young people it should be less than 2kPa and less than 4kPa in older people

Question 9

How to work out A-a gradient

Answer 9

PAO2 = PIO2 - PaCO2/0.8

PA02 = alveolar pressure of oxygen
PI02 = Room air (approx 20kPa)
PACO2 is virtually the same as arterial partial pressure of carbon dioxide