Isovolemic hemodilution consists of withdrawal of blood from the patient at the beginning
of a surgical procedure and its reinfusion at the end. It is most effective in cases in
which the anticipated surgical blood loss equals or exceeds 1,500 mL (generally 30
percent of the patient’s estimated blood volume). A minimum of two to three units of
blood must be collected for the procedure to be effective and the patient’s blood volume
is maintained isovolemically with crystalloid or, preferably, colloid solutions.
Hemodilution reduces red cell loss by lowering the hematocrit of the blood lost during
surgery. In addition, the autogeneic units contain viable platelets and coagulation
factors. Careful management of the fluid balance and monitoring of the patient’s cardiac
status are essential during this procedure. Low preoperative hemoglobin, infection,
coagulopathy, and significant cardiac, pulmonary, renal or hepatic disease rank among
the concerns and relative contraindications. Blood collected for isovolemic hemodilution
and stored at room temperature must be reinfused within eight hours of the start of
collection, while blood stored refrigerated may be reinfused within 24 hours of the start of
collection, provided that refrigerated storage was initiated within eight hours of the start
of collection.