|
Overview :
The hemoglobin alone should not be the sole criterion for
transfusion, since oxygen delivery is the critical issue. As a general rule of
thumb, one unit of RBCs raises the hemoglobin of average-size adult who is
anemic approximately 1 g/dL.
Default characteristics of packed red cell unit:
(1)
hematocrit 70-80%
• hemoglobin
= hematocrit / 2.941
(2) volume
about 250 mL after centrifugation
• addition
of preservative solutions (adenine-saline) may reduce the hematocrit to 60% and
increase the volume to 330 mL
• The volume
of pediatric quad (4 transfer) or quint (5 transfer) pack varies from 50 to 125
mL or more, depending on the nature of the transfer packs and needs of the
patient.
Default target hemoglobin based on rate of blood loss:
(1) acute: target 10 g/dL hemoglobin
(2) chronic: target 8 g/dL hemoglobin
Risk of volume overload:
(1) Look for a history of congestive heart failure or current
cardiac disease.
(2) Administer slow and monitor.
(3) Split units.
Massive transfusion:
(1) Look
for administration of volume of blood equal to or greater than blood volume.
(2) Monitor
for DIC
(3)
Administer FFP, cryoprecipitate and platelets based on fibrinogen, PT and
platelet count
Adult Quick and Dirty
Rules
number of units packed RBCs to transfuse in the normal adult
=
= (round to nearest whole number ((target hemoglobin) -
(current hemoglobin)))
Calculated
From the equation:
target hemoglobin in g/dL =
= (grams hemoglobin after transfusion) / (blood volume in
deciliters after transfusion) =
= (((hemoglobin before transfusion) * (blood volume in mL
before transfusion) / 100) + (((product hematocrit in percent) / 2.94) * (volume
of product in mL) / 100 * (number of products given))) / (((blood volume in mL
before transfusion) / 100) + ((volume of product in mL) / 100 * (number of
products given)))
where:
• A volume
in mL is divided by 100 to determine deciliters
•
Hematocrit divided by 2.94 gives hemoglobin.
• The
hematocrit for packed red cells is usually between 70 and 80%. It should not
exceed 80% since this results in insufficient preservative fluid for prolonged
storage.
• If there
has been an acute blood loss, then the patient's blood volume before transfusion
is the normal blood volume minus the volume of the blood loss.
• The
volume before transfusion plus volume of blood given is post-transfusion
volume.
The following equation can be derived:
number of packed red cells to give =
= ((blood volume before transfusion in mL) * ((target
hemoglobin) - (hemoglobin before transfusion))) / ((volume of product in mL) *
(((product hematocrit) / 2.94) - (target hemoglobin)))
Limitations:
• Initial
hemoconcentration or hemodilution can affect final hemoglobin.
Comments:
• Blood
replacement in surgery should not be based on estimates of blood loss, as this
typically results in unnecessary transfusion (Smetannikov 1996). Monitoring of
hemoglobin and/or hematocrit provides a more reliable guide to replacement
needs.
•
Preoperative expansion of circulating blood volume with clear fluids can help
decrease intraoperative hemoglobin loss.
|