Lecture 12-Hypoxia and Respiratory Failure Flashcards
True or false: tissues can be hypoxic without hypoxaemia
TRUE
What are the causes of hypoxia?
- low inspired O2
- hypoventilation
- ventilation/perfusion mismatch
- diffusion defect
- right to left shunt (eg tetralogy of Fallot)
What is type 1 respiratory failure?
- low pO2
- normal/low pCO2
What is type 2 respiratory failure?
- low pO2
- high pCO2
At what ventilation/perfusion (V/Q) ratio is gas exchange optimal?
1
What type of respiratory failure is hypoventilation and why?
Type 2 because hypoventilation always causes hypercapnia
What are the causes of acute hypoventilation?
- opiate overdose
- head injury
- very severe acute asthma
What is a cause of chronic hypoventilation?
COPD
What are the effects of hypoxaemia?
- impaired CNS function, confusion, irritability
- cardiac arrhythmias
- vasoconstriction of pulmonary vessels
- cyanosis
What are the compensatory mechanisms in chronic hypoxaemia?
-increased EPO from the kidney to increase Hb
What are the effects of hypercapnia?
- Respiratory acidosis
- impaired CNS function
- peripheral vasodilation
- cerebral vasodilation (headaches)
Why may treatment of hypoxia worsen hypercapnia?
O2 removes stimulus for hypoxic respiratory drive so alveolar ventilation decreases -> worsening hypercapnia
What happens to:
1) alveolar pO2
2) pCO2 when V/Q ratio < 1?
1) decreases
2) increases
What happens to
1) pO2
2) pCO2 when V/Q ratio > 1?
1) increases
2) decreases
Which conditions cause ventilation perfusion mismatch and why?
- asthma, pneumonia, RDS in newborns, pulmonary oedema, embolism
- because some alveoli are poorly ventilated
Why are conditions causing ventilation-perfusion mismatch classed as type 1 respiratory failure?
- 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
What are causes of diffuse lung fibrosis?
Conditions in which most alveoli are affected: asbestosis, pneumoconiosis
True or false: type 1 resp failure can progress to type 2
TRUE
