Lecture 12-Hypoxia and Respiratory Failure

Question 1

True or false: tissues can be hypoxic without hypoxaemia

Answer 1

TRUE

Question 2

What are the causes of hypoxia?

Answer 2

• low inspired O2
• hypoventilation
• ventilation/perfusion mismatch
• diffusion defect
• right to left shunt (eg tetralogy of Fallot)

Question 3

What is type 1 respiratory failure?

Answer 3

• low pO2

- normal/low pCO2

Question 4

What is type 2 respiratory failure?

Answer 4

• low pO2

- high pCO2

Question 5

At what ventilation/perfusion (V/Q) ratio is gas exchange optimal?

Answer 5

1

Question 6

What type of respiratory failure is hypoventilation and why?

Answer 6

Type 2 because hypoventilation always causes hypercapnia

Question 7

What are the causes of acute hypoventilation?

Answer 7

• opiate overdose
• head injury
• very severe acute asthma

Question 8

What is a cause of chronic hypoventilation?

Answer 8

COPD

Question 9

What are the effects of hypoxaemia?

Answer 9

• impaired CNS function, confusion, irritability
• cardiac arrhythmias
• vasoconstriction of pulmonary vessels
• cyanosis

Question 10

What are the compensatory mechanisms in chronic hypoxaemia?

Answer 10

-increased EPO from the kidney to increase Hb

Question 11

What are the effects of hypercapnia?

Answer 11

• Respiratory acidosis
• impaired CNS function
• peripheral vasodilation
• cerebral vasodilation (headaches)

Question 12

Why may treatment of hypoxia worsen hypercapnia?

Answer 12

O2 removes stimulus for hypoxic respiratory drive so alveolar ventilation decreases -> worsening hypercapnia

Question 13

What happens to:

1) alveolar pO2
2) pCO2 when V/Q ratio < 1?

Answer 13

1) decreases

2) increases

Question 14

What happens to

1) pO2
2) pCO2 when V/Q ratio > 1?

Answer 14

1) increases

2) decreases

Question 15

Which conditions cause ventilation perfusion mismatch and why?

Answer 15

• asthma, pneumonia, RDS in newborns, pulmonary oedema, embolism
• because some alveoli are poorly ventilated

Question 16

Why are conditions causing ventilation-perfusion mismatch classed as type 1 respiratory failure?

Answer 16

• V/Q < 1 (low pO2 and high pCO2) stimulates hyperventilation
• increased pO2 but Hb are fully saturated so O2 content is not significantly increased
• decreased pCO2 compensates for CO2 retention
• final result is low pO2 and normal pCO2 = type 1

Question 17

What are causes of diffuse lung fibrosis?

Answer 17

Conditions in which most alveoli are affected: asbestosis, pneumoconiosis

Question 18

True or false: type 1 resp failure can progress to type 2

Answer 18

TRUE