Pulmonary Gas Exchange Flashcards
What is FIO2?
Fraction of inspired air that is oxygen
What four abnormal states are associated with hypoxaemia?
Ventilation perfusion imbalance
Diffusion impairment
Alveolar hypoventilation
Shunt
What is the commonest cause of hypoxaemia clinically?
Low V/Q
What causes low V/Q in some alveoli?
It arises due to local alveolar hypoventilation due to some focal disease.
How does low V/Q respond to small increases in FIO2?
They respond well
What diseases can cause pathological shunt?
Arterial-venous malformations, congenital heart disease and pulmonary disease.
How do large shunts respond to increase in FIO2?
They respond poorly
In pneumonia, why do patients have hypoxaemia?
- Ventilation/perfusion mismatch (some ventilation of abnormal alveoli just not enough) - bronchitis/bronchopneumonia
- Shunt (no alveolar ventilation) - severe pneumonia
How can a fall in PaO2 be corrected?
It can be increased by raising the FIO2
Why do people get alveolar hypoventilation?
Upper airway and trachea obstruction
Mechanical problems with breathing mechanism
Functional problems with breathing mechanism
Neurological problems with breathing mechanism
What are examples of mechanical problems with breathing mechanism?
Chest wall damage
What are functional problems with breathing mechanism?
Muscle paralysis and diaphragmatic damage
What are neurological problems with breathing mechanism?
Peripheral nerve damage
CNS malfunction
Why might a patient with COPD have hypoxaemia?
- ventilation-perfusion mismatch (airway obstruction +/- bronchopneumonia)
- diffusion impairment (loss of alveolar surface area in emphysema)
- Alveolar hypoventilation - reduced respiratory drive
- Shunt - only during acute exacerbation if they’re pneumonia is extensive enough
Do diseases impairing gas diffusion affect CO2 levels?
No
