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Blood gases
Partial pressure of arterial oxygen (PaO2)
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This is the date the draft was written, not a medical review date.
The pressure of oxygen dissolved in arterial plasma, reflecting alveolar-capillary oxygen transfer. It falls with age and depends on the inspired oxygen fraction.
Reference interval
| Conventional (mmHg) | SI (kPa) | |
|---|---|---|
| Adults | 75–100 mmHg | 10–13.3 kPa |
Specimen: Arterial whole blood (heparinised syringe) · Conventional × 0.1333 = SI
Causes of high values
Supplemental oxygen therapy (expected), mechanical ventilation with high FiO2. Persistent hyperoxia may be harmful and is generally avoided.
Causes of low values
Hypoxaemia from hypoventilation, ventilation-perfusion mismatch (pneumonia, COPD, pulmonary embolism, asthma), shunt (ARDS, congenital heart disease), diffusion impairment, low inspired oxygen at altitude.
Pre-analytical and method notes
The 75 to 100 mmHg (10.0 to 13.3 kPa) interval applies to adults breathing room air at sea level; it falls with age and altitude, and a rough age-adjusted lower limit is often quoted. Always record FiO2, and note that venous or air-contaminated samples give misleading values. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
Related calculators
References
- Murray and Nadel's Textbook of Respiratory Medicine. Elsevier, 7th edition (2021) — Tier 3 (textbook)
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
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