In the oxygen content example, what is the absolute increase in O2 content when PaO2 rises from 120 to 150 with Hb 15 g/dL and SaO2 100%?

In the oxygen content example, what is the absolute increase in O2 content when PaO2 rises from 120 to 150 with Hb 15 g/dL and SaO2 100%?

• A. 0.01
• B. 0.09
• C. 0.9
• D. 9.0

Answer: (B)

Oxygen content has two parts: oxygen bound to hemoglobin and dissolved oxygen in plasma. The bound portion stays the same when hemoglobin concentration and saturation don’t change, while the dissolved portion depends on PaO2. Use CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2). With Hb 15 g/dL and SaO2 100% (1.0): - Bound O2 = 15 × 1.34 × 1.0 = 20.1 mL O2 per dL (unchanged). - Dissolved O2 changes from 0.003 × 120 = 0.36 to 0.003 × 150 = 0.45 mL O2 per dL. Absolute increase = 0.45 − 0.36 = 0.09 mL O2 per dL. So the increase in O2 content is 0.09 mL/dL.

Oxygen content has two parts: oxygen bound to hemoglobin and dissolved oxygen in plasma. The bound portion stays the same when hemoglobin concentration and saturation don’t change, while the dissolved portion depends on PaO2.

Use CaO2 = (Hb × 1.34 × SaO2) + (0.003 × PaO2).

With Hb 15 g/dL and SaO2 100% (1.0):

• Bound O2 = 15 × 1.34 × 1.0 = 20.1 mL O2 per dL (unchanged).

• Dissolved O2 changes from 0.003 × 120 = 0.36 to 0.003 × 150 = 0.45 mL O2 per dL.

Absolute increase = 0.45 − 0.36 = 0.09 mL O2 per dL.

So the increase in O2 content is 0.09 mL/dL.