Normal PaO2 Values
The normal range for partial pressure of arterial oxygen (PaO2) in healthy adults is 10.9-14.8 kPa (80-110 mmHg), with variations based on age. 1
Age-Related Normal PaO2 Values
- For young adults aged 18-24 years, the mean PaO2 is 13.4 kPa (100.5 mmHg) with a normal range of 12.0-14.8 kPa (90-111 mmHg) 1
- For adults aged 25-34 years, the mean PaO2 is 13.4 kPa (100.5 mmHg) with a normal range of 12.1-14.7 kPa (91-110 mmHg) 1
- For adults aged 35-44 years, the mean PaO2 is 13.2 kPa (99 mmHg) with a normal range of 11.1-15.2 kPa (83-114 mmHg) 1
- For adults aged 45-54 years, the mean PaO2 is 13.0 kPa (97.5 mmHg) with a normal range of 10.9-15.1 kPa (82-113 mmHg) 1
- For adults aged 55-64 years, the mean PaO2 is 12.1 kPa (90.7 mmHg) with a normal range of 10.9-13.3 kPa (82-100 mmHg) 1
- For adults over 64 years, the mean PaO2 is 11.9 kPa (89.2 mmHg) with a normal range of 9.0-14.8 kPa (68-111 mmHg) 1
Clinical Significance of PaO2
- PaO2 below 8.0 kPa (60 mmHg) is considered hypoxemia, with increased risk of tissue hypoxia 1
- PaO2 below 8.0 kPa (60 mmHg) is associated with poor outcomes in patients with traumatic brain injury 2
- There is no known risk of hypoxic tissue injury with PaO2 above 8.0 kPa (60 mmHg) 1
- PaO2 values decrease with increasing altitude due to lower barometric pressure 1, 3
- At sea level, PaO2 is primarily determined by lung function and represents oxygen diffusion within the lungs 4
Factors Affecting PaO2
- Age: PaO2 decreases with advancing age, with a more pronounced decline after age 55 1
- Altitude: PaO2 decreases approximately 0.84 kPa (6.3 mmHg) per 1000m increase in altitude in patients with COPD, and likely more in healthy individuals 5
- Position: Upright position can affect PaO2 in certain conditions like hepatopulmonary syndrome 1
- Respiratory diseases: Conditions affecting ventilation-perfusion matching, diffusion capacity, or alveolar ventilation can reduce PaO2 1
- Barometric pressure: Changes in atmospheric pressure directly affect the inspired oxygen partial pressure 1
Clinical Applications
- PaO2 measurement requires arterial blood gas analysis 6
- PaO2 should be interpreted alongside oxygen saturation (SaO2) and hemoglobin concentration to assess oxygen content and delivery 4
- For air travel assessment in patients with respiratory disease, a PaO2 below 6.7 kPa (50 mmHg) at cabin altitude (equivalent to breathing 15.1% oxygen at sea level) may require supplemental oxygen 1
- PaO2/FiO2 ratio is an important parameter for assessing severity of acute respiratory distress syndrome and predicting outcomes 7
Important Considerations
- PaO2 alone does not determine tissue oxygenation, which also depends on hemoglobin concentration, cardiac output, and tissue oxygen extraction 1, 4
- Normal PaO2 with low oxygen saturation may indicate abnormal hemoglobin (e.g., methemoglobinemia) 4
- PaO2 should be interpreted alongside PaCO2 (normal range 4.6-6.1 kPa or 34-46 mmHg) to assess respiratory function 6
- Hypoxemia (low PaO2) is just one cause of tissue hypoxia; others include anemic hypoxia, stagnant hypoxia, and histotoxic hypoxia 1