An arterial blood sample shows haemoglobin 15 g/dL, SaO2 100%, and PaO2 100 mmHg. How much oxygen is carried per 100 mL of this blood in physical solution?
- A 3.0 mL
- B 1.34 mL
- C 0.3 mL ✓
- D 0.03 mL
Correct answer: C. 0.3 mL
Explanation
Dissolved oxygen follows Henry's law: 0.003 mL O2 per dL per mmHg of PO2. At a PaO2 of 100 mmHg this gives 0.3 mL/dL, a trivial amount compared with roughly 20 mL/dL bound to haemoglobin (1.34 mL per gram times 15 g/dL). Option D confuses the coefficient itself, and option A would apply at a PaO2 near 1000 mmHg, as in hyperbaric oxygenation.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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