Normal PO2 Values
The normal range for partial pressure of arterial oxygen (PaO2) is 11.0-14.8 kPa (80-110 mm Hg) in healthy young adults at sea level, with values declining progressively with age. 1
Age-Specific Normal Ranges
The normal PaO2 varies significantly by age, and clinicians must use age-appropriate reference values when interpreting arterial blood gases:
- Ages 18-24 years: Mean 13.4 kPa (100 mm Hg), range 12.0-14.8 kPa (90-111 mm Hg) 1, 2
- Ages 25-34 years: Mean 13.4 kPa (100 mm Hg), range 12.1-14.7 kPa (91-110 mm Hg) 1, 2
- Ages 35-44 years: Mean 13.2 kPa (99 mm Hg), range 11.1-15.2 kPa (83-114 mm Hg) 1, 2
- Ages 45-54 years: Mean 13.0 kPa (98 mm Hg), range 10.9-15.1 kPa (82-113 mm Hg) 1, 2
- Ages 55-64 years: Mean 12.1 kPa (91 mm Hg), range 10.9-13.3 kPa (82-100 mm Hg) 1, 2
- Ages >64 years: Mean 11.9 kPa (89 mm Hg), range 9.0-14.8 kPa (68-111 mm Hg) 1, 2
Clinical Thresholds for Hypoxemia
Understanding when PaO2 becomes pathologically low is critical for clinical decision-making:
- PaO2 <8.0 kPa (60 mm Hg) defines hypoxemia and represents the threshold below which tissue hypoxia risk increases 1, 2
- No known risk of hypoxic tissue injury exists above 8.0 kPa (60 mm Hg) 2
- This corresponds to an oxygen saturation (SaO2) of approximately 90% on the oxyhemoglobin dissociation curve 1
Target Range in Acute Care Settings
In critically ill patients requiring intervention, specific PaO2 targets should be maintained:
- Maintain PaO2 between 60-100 mm Hg (8.0-13.3 kPa) during interventions for life-threatening hemorrhage or emergency neurosurgery 1
- This range balances adequate tissue oxygenation while avoiding potential hyperoxia-related complications 1
Important Clinical Considerations
Age-related decline: The progressive decrease in PaO2 with advancing age is physiologically normal and reflects changes in ventilation-perfusion matching and chest wall mechanics 1. The decline becomes more pronounced after age 55 years 2.
Position effects: PaO2 measurements are typically obtained with patients at rest in a seated or supine position 1. Values may differ with position changes, particularly in certain disease states.
Altitude adjustment: These normal values apply at sea level; PaO2 decreases at higher altitudes due to reduced barometric pressure 2.
Oxygen saturation correlation: While PaO2 and SaO2 are related, they provide complementary information. The normal SaO2 range for young adults (18-24 years) is 96.1-97.7%, declining to 92.7-98.3% in those >64 years 1.
Common Pitfalls to Avoid
Do not assume a single "normal" value applies to all ages—always use age-adjusted reference ranges when interpreting PaO2 results 1, 2.
Do not rely solely on PaO2 to assess tissue oxygenation—hemoglobin concentration, cardiac output, and tissue oxygen extraction also determine oxygen delivery 2.
Do not interpret PaO2 in isolation—always evaluate it alongside PaCO2 (normal range 4.6-6.1 kPa or 34-46 mm Hg) and pH to fully assess respiratory and acid-base status 1, 3.