If PaO2 increases significantly while SaO2 remains 100%, which component of O2 content increases?

If PaO2 increases significantly while SaO2 remains 100%, which component of O2 content increases?

• A. Bound O2
• B. Dissolved O2
• C. Both
• D. None

Answer: (B)

Oxygen content in arterial blood has two parts: dissolved oxygen in plasma and oxygen bound to hemoglobin. SaO2 reflects how much hemoglobin is saturated, and PaO2 reflects the amount dissolved in plasma. If PaO2 rises but SaO2 is already 100%, the bound portion cannot increase further because hemoglobin is fully saturated. The only part that increases is the dissolved oxygen, which rises as PaO2 increases (Henry’s law). This relationship is captured in CaO2 ≈ (Hb × 1.34 × SaO2) + (0.003 × PaO2); with SaO2 at 100%, the first term is fixed, and the second term grows with PaO2, raising the total oxygen content via dissolved O2.

Oxygen content in arterial blood has two parts: dissolved oxygen in plasma and oxygen bound to hemoglobin. SaO2 reflects how much hemoglobin is saturated, and PaO2 reflects the amount dissolved in plasma. If PaO2 rises but SaO2 is already 100%, the bound portion cannot increase further because hemoglobin is fully saturated. The only part that increases is the dissolved oxygen, which rises as PaO2 increases (Henry’s law). This relationship is captured in CaO2 ≈ (Hb × 1.34 × SaO2) + (0.003 × PaO2); with SaO2 at 100%, the first term is fixed, and the second term grows with PaO2, raising the total oxygen content via dissolved O2.