13 Hypoxia and Respiratory Failure

Question 1

Differentiate between hypoxia and hypoxaemia

Answer 1

Question 2

Give examples of when a patient might be hypoxic but not hypoxaemic

Answer 2

• Severe anaemia
• Poor perfusion

Question 3

What is respiratory failure? Differentiate between Type 1 an Type 2 respiratory failure.

Answer 3

Respiratory failure= pO₂< 8kPa when breathing air at sea level

Question 4

What systemic effects does hypoxia have?

Answer 4

Question 5

What systemic effects does hypercapnia have?

Answer 5

Question 6

What are the causes of hypoxaemia? (5)

Answer 6

Question 7

What effects does chronic hypoxaemia have?

Answer 7

Question 8

Explain why someone who is acutely exposed to high altitudes (atmospheric pressue <101kPa) will have a low pO₂ and low pCO_2.

Answer 8

Low inspired pO₂ level

Peripheral chemoreceptors stimulated

–> Hyperventilation– causes low pCO₂

Question 9

What adaptations does someone who lives at high altitudes have?

Answer 9

• Polycythaemia
• Increased 2-3 DPG
• Increased capillary density

Question 10

Is hypoventilation a type 1 or type 2 respiratory failure? Why?

Answer 10

Type 2

Elevated pCO₂

(Artificial ventilation required)

Question 11

Give some causes of hypoventilation.

Answer 11

Question 12

Explain why a patient with with COPD will not require ventilatory support until the later stages of the condition.

Answer 12

Time allowed for some compensatory mechanisms to develop

(May need ventilation during acute complications eg lung infection)

Question 13

Outline how the body responds to chronic hypercapnia. (Kidney and Central chemoreceptors)

Answer 13

Kidney: renal compensation of respiratory acidosis

Central chemoreceptors: Choroid complex imports HCO₃^- into CSF. Restores CSF pH to normal. Central chemoreceptors ‘reset’

Question 14

How would you treat hypoxia in a patient with chronic type 2 respiratory failure?

Check bicarb- may be only sign of CO₂ retention

Answer 14

Controlled oxygen therapy- avoid risk of worsening hypercapnia

Question 15

Explain how a V/Q mismatch (due to poor ventilation of alveoli/pulmonary embolism) leads to Type 1 respiratory failure.

(eg COPD-early stages, asthma, RDS, pneumonia, pulmonary embolism)

Answer 15

• Drop in pO₂
• Hyperventiation stimulated- increased CO₂ removal
• Hyperventilation insufficient to correct fall in pO₂

Question 16

Explain why a diffusion impairment within the alveoli causes type 1 respiratory failure and not type 2.

Answer 16

O₂ diffuses less readily than CO₂ - always affected more by any change in diffusion barrier

Question 17

Give an example of a condition which can initally cause Type 1 respiratory failure that can progress to Type 2 respiratory failure and explain how this happens

Answer 17

Asthma

More and more airways- narrowed, exhaustion sets in

Ventilatory support required

Question 18

Explain why treating a hypoxic patient with uncontrolled oxygen can only worsen hypercapnia. (2 mechanisms)

How should it be controlled instead?

Answer 18

Controlled oxygen therapy- continuously monitor oxygen and CO₂ levels

Question 19

What is a patient going to require if controlled oxygen therapy still causes hypercapnia?

Answer 19

Assisted ventilation