|
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.
|