packed red blood cell volume in mL =
= ((hematocrit desired in percent) – (hematocrit pretransfusion in percent)) * (total blood volume in mL) / (hematocrit of packed red cell product in percent)
where:
• The usual hematocrit for a packed red cell product is 70-80%.
• A rough estimate of total blood volume in children is 80 mL/kg and in adults is 65 mL/kg. Males tend to have a slightly greater blood volume than females. A person at the extremes of body weight would need a more explicit equation (see Chapter 2).
percent hemoglobin S after transfusion =
= (percent hemoglobin S before transfusion) * (1 – (X / (Y + X))) =
= (percent hemoglobin S before transfusion) * (Y / (X + Y))
Y =
= (total blood volume in mL) * (hematocrit pretransfusion in percent)
X =
= (packed red cell volume transfused in mL) * (hematocrit of packed red cell product in percent)
When I worked through this equation in conjunction with the equation for packed red blood cell volume, I got:
percent hemoglobin S after transfusion =
= (percent hemoglobin S before transfusion) * (hematocrit pretransfusion) / (hematocrit desired)
