What does the factor 1.34 represent in the oxygen content formulas?

• A. The milliliters of oxygen dissolved per liter of blood
• B. The milliliters of oxygen carried by one gram of hemoglobin when fully saturated
• C. The amount of oxygen bound to carbon dioxide
• D. The metabolic oxygen requirement per minute

Answer: (B)

The number 1.34 is the amount of oxygen that one gram of hemoglobin can carry when the hemoglobin is fully saturated with oxygen. In the standard oxygen content formula CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2), this constant represents the oxygen-binding capacity of hemoglobin per gram. So, for each gram of Hb, once fully saturated, about 1.34 mL of O2 is transported with the blood. The dissolved oxygen term (0.003 × PaO2) is much smaller, since only a tiny amount of O2 dissolves in plasma. This makes the Hb-bound portion mainly determine the arterial oxygen content. Thus the factor 1.34 is best understood as the oxygen-carrying capacity of hemoglobin per gram when saturated.