Oxygen Extraction Ratio (O2ER) represents which of the following?

Oxygen Extraction Ratio (O2ER) represents which of the following?

• A. The percentage of bound oxygen that is not released
• B. The percentage of carried oxygen bound to hemoglobin
• C. The percentage of delivered oxygen that is extracted and consumed by the tissues
• D. The ratio of CaO2 to CvO2

Answer: (C)

Oxygen Extraction Ratio measures how much of the oxygen delivered to the tissues is actually taken up and used. It’s the fraction of arterial oxygen content that is removed by the tissues, reflecting the balance between oxygen delivery and consumption. The standard way to express it is (CaO2 − CvO2) / CaO2, which also ties to oxygen consumption (VO2) and delivery (DO2) through VO2 = DO2 × O2ER. Clinically, it tells you how hard the tissues are working to extract oxygen; a higher O2ER means more extraction is occurring, often because delivery is limited or metabolic demand is high, whereas a lower value suggests adequate delivery with less extraction. The other statements don’t describe this extraction process: one refers to oxygen that remains bound and not released, another to the portion bound to hemoglobin, and the last is just a ratio of arterial to venous oxygen content without expressing the fraction actually extracted.

Oxygen Extraction Ratio measures how much of the oxygen delivered to the tissues is actually taken up and used. It’s the fraction of arterial oxygen content that is removed by the tissues, reflecting the balance between oxygen delivery and consumption. The standard way to express it is (CaO2 − CvO2) / CaO2, which also ties to oxygen consumption (VO2) and delivery (DO2) through VO2 = DO2 × O2ER. Clinically, it tells you how hard the tissues are working to extract oxygen; a higher O2ER means more extraction is occurring, often because delivery is limited or metabolic demand is high, whereas a lower value suggests adequate delivery with less extraction. The other statements don’t describe this extraction process: one refers to oxygen that remains bound and not released, another to the portion bound to hemoglobin, and the last is just a ratio of arterial to venous oxygen content without expressing the fraction actually extracted.