Overview
The PaO₂ is the partial pressure of oxygen dissolved in plasma. This is a marker of the amount of oxygen available to be delivered to tissues, and a reduced PaO₂ is indicative of hypoxia.
Normal Range
- 80-100mmHg on room air
Hypoxia
Causes of Hypoxia
Low Partial Pressure of O₂
- High altitude
Hypoventilation
- CNS - drugs, trauma, encephalopathy, MND, Guillain-Barré
- Muscular / neuromuscular - myaesthenia, paralytics, myopathy, fatigue, malnutrition
- Airway obstruction
- Decreased compliance
- Chest wall abnormalities
V/Q Mismatch
- Physiological shunt - atelectasis, pulmonary oedema, pneumonia, ARDS
- Anatomical shunt - cardiac shunt e.g. tetralogy of Fallot
- Dead space - asthma, COPD, pulmonary embolus, heart failure
Decreased Diffusion Capacity
- Rare
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