An arterial sample shows hemoglobin 15 g/dL, SaO2 97%, PaO2 100 mmHg, and dissolved oxygen contribution of 0.3 mL/dL. The total arterial oxygen content (CaO2) is closest to:

• A 12.0 mL O2 per dL
• B 15.7 mL O2 per dL
• C 19.8 mL O2 per dL ✓
• D 24.6 mL O2 per dL

Explanation

CaO2 = (1.34 x Hb x SaO2) + (0.003 x PaO2). Here 1.34 x 15 x 0.97 = 19.5 mL/dL bound oxygen, plus about 0.3 mL/dL dissolved, giving roughly 19.8 mL/dL. Each gram of hemoglobin carries about 1.34 mL of oxygen when fully saturated, and dissolved oxygen contributes negligibly at normal PaO2. Option B ignores saturation arithmetic errors and option D assumes supraphysiologic carrying capacity.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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