At 4500 m altitude, an acclimatized climber has PaO2 of 48 mmHg and hemoglobin of 18 g/dL with 85 percent oxygen saturation. What is the approximate arterial oxygen content (CaO2)? (Use: CaO2 = [1.34 x Hb x SaO2] + [0.003 x PaO2])

• A 15.2 mL O2/dL
• B 18.5 mL O2/dL
• C 20.7 mL O2/dL ✓
• D 24.1 mL O2/dL

Explanation

CaO2 = (1.34 x 18 x 0.85) + (0.003 x 48) = 20.502 + 0.144 = approximately 20.65 mL O2/dL. Dissolved oxygen contributes negligibly. Polycythemia (elevated Hb) compensates for low SaO2, maintaining oxygen content near sea-level values. The 15.2 option likely ignores the hemoglobin elevation, and 24.1 overestimates by assuming full saturation.

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

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