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.



(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)



• 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 blood 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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