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Overview :
A patient with a hemoglobinopathy, aplastic anemia,
myelodysplastic syndrome or other chronic anemia may require regular
transfusions. The transfusion requirement for the patient can be calculated
based on laboratory testing and transfusion-related factors. The authors are
from Arthus Amtssygehus in Denmark.
transfusion requirement as grams hemoglobin per month =
= ((((initial pretransfusion hemoglobin in g/L) * (blood
volume in liters))+ ((number of blood units transfused) * 75)) -
((pretransfusion hemoglobin in g/L prior to next transfusion) * (blood volume in
liters))) / (number of days between transfusions) * 31
The blood volume was calculated using equations from
Ganong:
plasma volume in liters =
= (body weight in kilograms) * 0.045
blood volume in liters =
= (plasma volume in liters) * 100 / (100 - (hematocrit))
where:
• 75
indicates the mean hemoglobin in 1 unit of packed RBCs as g per unit. A normal
person should have a hemoglobin of about 140-150 g per liter. 1 unit of packed
RBCs is made from 500 mL of blood, or 70-75 g.
• The
equation from 1992 used 8.7 grams hemoglobin per unit rather than the 75 used in
the later form.
• 31
indicates the number of days in a month.
• As
discussed in Chapter 2 (02.10.05) the whole body hematocrit should be used. This
equals 0.91 * (venous hematocrit).
• Blood
volume could probably be calculated before each transfusion but I will treat it
as constant just to keep the calculations simple.
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