Blood Gas
Partial Pressure of Oxygen (pO2)
pO2 is the partial pressure of oxygen dissolved in blood plasma, measured amperometrically by point-of-care blood gas analysers. It indicates how effectively oxygen is transferring from the lungs into arterial blood and is a core component of arterial blood gas assessment.
Why it is measured
Clinicians use pO2 to gauge oxygenation and the severity of respiratory failure, to guide oxygen therapy and ventilation, and to monitor acutely unwell patients. Because pO2 reflects only the small dissolved fraction of oxygen, it is interpreted alongside oxygen saturation and haemoglobin.
| Typical range | Indicative adult arterial pO2 is approximately 10.0 to 13.3 kPa (75 to 100 mmHg) breathing room air, with values falling gradually as age increases. Venous and capillary pO2 are substantially lower and are not interchangeable with arterial values. Ranges vary by method, sample type, altitude and inspired oxygen, so always apply local, method-specific reference intervals. |
|---|---|
| Sample | Arterial whole blood collected into a heparinised (balanced or lithium heparin) syringe, air expelled, mixed well and analysed promptly. Venous or capillary whole blood is sometimes used but is interpreted differently for oxygenation. |
| Turnaround | Typically under 1 to 2 minutes at the point of care, with results available alongside the rest of the blood gas panel in a single run. |
Point of care devices that report it
- Abbott i-STAT (CG8+, CG4+ and G3+ cartridges)
- Siemens Healthineers epoc Blood Analysis System
- Radiometer ABL90 FLEX and ABL9
- Werfen GEM Premier 5000
- Nova Biomedical Stat Profile Prime Plus
Questions, answered
What is the difference between pO2 and oxygen saturation (SpO2 or SaO2)?
pO2 measures the pressure of oxygen dissolved in plasma, whereas saturation measures the percentage of haemoglobin that is bound to oxygen. They are linked through the oxygen dissociation curve but are not the same measurement, so they provide complementary information and are best reviewed together rather than in isolation. This is general education and not a substitute for clinical assessment.
Can pO2 be measured from a venous or capillary sample?
Blood gas analysers can report pO2 on venous or capillary blood, but venous pO2 is much lower than arterial pO2 and the two are not interchangeable for assessing oxygenation. Arterial sampling remains the reference for pO2, so the sample type should always be recorded clearly and considered when reviewing the result.
How does sample handling affect the pO2 result?
pO2 is sensitive to pre-analytical factors. Residual air bubbles, delayed analysis and inappropriate storage can shift the measured value, so air should be expelled promptly, the sample mixed thoroughly and analysed quickly following the local protocol. Good technique and routine quality control help keep pO2 results reliable.