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Overview :
Davies et al used an equation to estimate the required volume
of blood to be transfused into a child to achieve a desired increment in
hemoglobin. The authors are from Bristol Royal Infirmary in England.
Parameters:
(1) intended increment in hemoglobin in g/dL
(2) hematocrit of blood product as a decimal fraction
(3) body weight of the child in kilograms
intended increment in hemoglobin =
= (desired hemoglobin) - (current hemoglobin)
blood volume to transfuse in mL =
= (body weight in kilograms) * (target increment in
hemoglobin) * 3 / (hematocrit of the blood product)
where:
• The
simple relation between hemoglobin and hematocrit is: hemoglobin = (hematocrit
in percent) / 3.
• A portion
of the expression appears to be calculating the hemoglobin content of the blood
product. Body weight is often used in children to estimate the blood volume.
• The
hematocrit for blood products reported by the authors for England is 0.6 (range
0.55 to 0.65). US blood products may have a hematocrit that is slightly higher (0.7 to
0.8).
•
Postoperative monitoring can be done at 1 hour after the transfusion is
completed. Hemoglobin levels after replacement are stable unless there is
bleeding or hemolysis.
Children were excluded from the study if they had a condition
that might confound the analysis due to increased red bllod loss and/or
hemodilution:
(1) active bleeding or blood loss from drains
(2) active hemolysis
(3) infusion of crystalloid or colloid
(4) dialysis or ECMO
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