Physiologic And Monitoring Practice Test

CaO2 includes the dissolved oxygen term in addition to oxygen bound to hemoglobin.

CaO2 is based only on SaO2 and Hb. CaO2 depends only on Hb. CaO2 ignores PaO2. CaO2 includes the dissolved oxygen term 0.003 × PaO2 in addition to the oxygen bound to Hb.

Correct Answer:

CaO2 includes the dissolved oxygen term 0.003 × PaO2 in addition to the oxygen bound to Hb.

Explanation:

Arterial oxygen content is the sum of two parts: oxygen bound to hemoglobin and oxygen dissolved in plasma. The bound portion depends on how much hemoglobin there is and how saturated it is with oxygen, calculated as Hb concentration times 1.34 mL O2 per gram times SaO2. The dissolved portion, though smaller, comes from oxygen freely dissolved in plasma and is proportional to PaO2 with a solubility of about 0.003 mL O2 per dL of blood per mmHg. Put together, CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003). This is why including the dissolved oxygen term 0.003 × PaO2 in addition to the Hb-bound oxygen correctly describes CaO2. The dissolved term ensures PaO2 contributes to overall oxygen content, not just saturation and Hb amount.

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