TYK73
When comparing a normal adult with a normal fetus, which of the following are true?
A. The oxygen content of the blood is similar for both
B. The oxygen content of the blood is lower for the fetus
C. The oxygen content of the blood is higher for the fetus
D. A fetus is just a small adult
Answer
The answer is A.
Remember, I am asking about OXYGEN CONTENT of the blood, not saturation or oxygen delivery. They are not the same.
Oxygen content is calculated from the oxygen content equation. Because at normal PaO2 levels, the amount of dissolved oxygen is negligible and can be ignored for this example. A typical adult will have a saturation of 98-100% and a hemoglobin of 10-11. Using the oxygen content equation gives the following oxygen content. CaO2 = 1.0 (saturation) × 11 (Hgb) × 1.34 = 14.7 mL O2 / dL of blood The fetus has a higher hemoglobin but a lower oxygen saturation. Using the equation for a normal fetus (Hgb =16-17 and saturation of 65%) in the oxygen content equation gives the following CaO2 =0.65 (saturation) ×17(Hgb) ×1.34=14.8mL O2/dL of blood Even though the oxygen content is the same, the oxygen delivery is not. Given the fetal hemoglobin's increased affinity of oxygen, the oxygen delivery (offloading) to the target tissues is decreased.
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