blood gases and oxygenation
Last reviewed 01/2018
The normal range for PaO2 is 11.3-13.3 kPa. A partial pressure less than 8 kPa defines respiratory failure.
Arterial hypoxaemia is commonly due to pulmonary disease:
- poor gas transfer:
- type I respiratory failure
- PaCO2 is typically low
- hypoventilation:
- type II respiratory failure
- PaCO2 is typically raised
Arterial hypoxaemia may occur when the lungs are normal:
- low inspired partial pressure of oxygen e.g. altitude
- ventilation-perfusion mismatch
- right to left shunts:
- congenital heart disease
- arteriovenous malformation of the pulmonary vessels
Measurement of the alveolar-arterial (A-a) gradient is useful in hypoxic patients and may help to distinguish hypoxaemia due to pulmonary disease from other causes of hypoxaemia.