Quick Answer: Using the Hüfner constant, each gram of hemoglobin carries ~1.34 mL of O₂. At Hb = 10 g/dL, oxygen-carrying capacity = 10 × 1.34 = 13.4 mL/100 mL blood, which rounds to approximately 13 mL. The answer is B. 13 mL of oxygen.
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Answer: B. 13 mL of oxygen
The Hufner Constant and Oxygen-Carrying Capacity
The oxygen-carrying capacity of blood depends almost entirely on hemoglobin (Hb). The key formula is:
O₂ Content (CaO₂) = Hb (g/dL) × 1.34 mL O₂/g Hb × SaO₂
The Hufner constant (1.34 mL/g, sometimes approximated as 1.36 mL/g) represents the maximum volume of oxygen that each gram of hemoglobin can carry when fully saturated.
Calculation
Assuming full saturation (SaO₂ = 100%):
CaO₂ = 10 g/dL × 1.34 mL O₂/g = 13.4 mL O₂ per 100 mL blood
This rounds to approximately 13 mL, making option B correct.
Why Not the Others?
| Option | Value | Corresponds to Hb level |
|---|---|---|
| A | 20.7 mL | ~15.4 g/dL (normal male Hb × 1.34) |
| B | 13 mL | 10 g/dL × 1.34 = 13.4 mL ✓ |
| C | 10 mL | ~7.5 g/dL |
| D | 7.4 mL | ~5.5 g/dL |
Key Points to Remember
- Normal Hb (~15 g/dL) carries ~20.1 mL O₂ per 100 mL blood
- At Hb = 10 g/dL (anemia), carrying capacity drops proportionally to ~13 mL
- A small additional amount (~0.3 mL) is dissolved in plasma (Henry's law), but this is negligible unless O₂ partial pressure is very high (as in hyperbaric oxygen therapy)
- The formula confirms that oxygen delivery is directly proportional to Hb concentration - Ganong's Review of Medical Physiology and Barash's Clinical Anesthesia both use CaO₂ = Hb × 1.34 × SaO₂ as the standard formula
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