In the O2 content equation, what does the coefficient 0.003 represent?

In the O2 content equation, what does the coefficient 0.003 represent?

• A. Bound O2
• B. Dissolved O2
• C. Carbon dioxide content
• D. pH influence

Answer: (B)

The number 0.003 in the O2 content equation represents the dissolved oxygen in plasma. This term comes from Henry’s law, which says a gas’s amount that dissolves in a liquid is proportional to its partial pressure. In the equation for arterial O2 content (CaO2), the dissolved portion is PaO2 × 0.003, giving the amount of O2 that is physically dissolved in the blood, independent of hemoglobin. For example, with a PaO2 of 100 mmHg, the dissolved O2 is 0.003 × 100 = 0.3 mL O2 per deciliter of blood. This dissolved amount is small compared with the O2 bound to hemoglobin (which is 1.34 mL O2 per gram of Hb times Hb concentration times SaO2), but it’s essential for determining how much O2 is actually present in blood, especially when hemoglobin is low or SaO2 drops. So the coefficient 0.003 specifically denotes the solubility of O2 in plasma (dissolved O2 per mmHg of PaO2), not bound O2, CO2 content, or pH effects.

The number 0.003 in the O2 content equation represents the dissolved oxygen in plasma. This term comes from Henry’s law, which says a gas’s amount that dissolves in a liquid is proportional to its partial pressure. In the equation for arterial O2 content (CaO2), the dissolved portion is PaO2 × 0.003, giving the amount of O2 that is physically dissolved in the blood, independent of hemoglobin.

For example, with a PaO2 of 100 mmHg, the dissolved O2 is 0.003 × 100 = 0.3 mL O2 per deciliter of blood. This dissolved amount is small compared with the O2 bound to hemoglobin (which is 1.34 mL O2 per gram of Hb times Hb concentration times SaO2), but it’s essential for determining how much O2 is actually present in blood, especially when hemoglobin is low or SaO2 drops.

So the coefficient 0.003 specifically denotes the solubility of O2 in plasma (dissolved O2 per mmHg of PaO2), not bound O2, CO2 content, or pH effects.