Explain how oxygen supply is maintained to the tissues in chronic anaemia.
Candidates were expected to base their answer around the variables involved in the equations that describe oxygen content in blood and oxygen delivery. Although most candidates mentioned changes in haemoglobin that increase oxygen carriage, a more complete discussion of the changes that influence cardiac output and the peripheral circulation was often omitted
Total blood oxygen delivery (DO2) = CO × CaO2,
and CaO2 = (sO2 × ceHb × BO2 ) + (PaO2 × 0.03)
Where the ceHb is in decline, the other variables which describe CaO2 are usually not susceptible to large-scale change, and therefor the cardiac output needs increase.
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