MLT GlobePartial pressure of oxygen (pO₂)
Blood Gases · also called PaO2, pO2
What it measures
pO₂ measures oxygen dissolved in arterial plasma and reflects how well the lungs transfer oxygen to blood. It is used to diagnose hypoxaemia and adjust oxygen therapy and ventilation.
Specimen and preparation
- Specimen: Arterial blood in a heparinised (balanced lithium heparin) syringe
- Tube: Other top
- Preparation: Expel air bubbles, cap immediately, mix well and analyse within 30 minutes (ideally 15) at room temperature in a plastic syringe; do not ice plastic syringes, and use a glass syringe on ice only if longer delay is unavoidable. Record FiO₂ and temperature.
Reference range
| Group | Range |
|---|---|
| Arterial, room air (adult) | 80–100 (10.7–13.3) mmHg (kPa) |
| Arterial, age >70 | ≥70 (≥9.3) mmHg (kPa) |
Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.
Causes of high values
- Supplemental oxygen
- Hyperventilation
- Air bubble in sample
Causes of low values
- Pneumonia, ARDS, pulmonary oedema
- COPD and asthma
- Pulmonary embolism
- Hypoventilation
- Venous sample or very high white cell count (artefact)
Method
Clark polarographic or optical oxygen electrode
Good to know
PaO₂ below 60 mmHg (8 kPa) defines respiratory failure. The PaO₂/FiO₂ ratio grades ARDS severity.
Related tests
📱 Practise with a timer, track your score and earn certificates in the free MLT Globe app – Google Play or practise online.