In this article we will take a look at what this procedure is and what is involved.
What is hemodilution?
Acute normovolemic hemodilution, ANH, is a blood conservation technique that was introduced in the 1970's. This procedure entails removing blood from a patient either before or immediately after the induction of anesthesia during surgery. The procedure involves the maintenance of isovolemia using a crystalloid and/or colloid replacement. The amount of blood removed is usually is one to three units (450 ml approximately is one unit. Or about one half a liter bottle of soda.)
The blood is then anticoagulated and maintained in the operation room for up to eight hours. Is is then reinfused into the patient as needed during the surgical procedure. (Please note that Jehovah's Witnesses will not allow the blood to be saved for a later procedure, due to their belief in the sanctity of blood. The blood must remain part of a continuous closed circuit.)
Who can accept this procedure?
ANH should be used by patients with a good hematocrit and who are expected to lose more than two units (900ml) of blood during surgery. It is better tolerated in young, healthy people but has been used in the elderly, depening on the procedure.
Hemodilution would be contraindicated in the following procedures:
Cardiac disease
Impaired renal function
Baseline Hgb less than 11g/dl
Low concentration of coagulation proteins
Inadequate vascular access
Absence of adequate monitoring
Finally, hemodilution may be used alone, or in combination with other blood conservation techniques.
Vocabulary
Anticoagulant - A substance that prevents the blood from clotting.
Colloid - A substance microscopically dispersed evenly throughout another.
Crystalloid - A substance that can pass through a semi-permeable membrance and crystallize.
Hematocrit - Ratio of volume occupied by packed red blood cells to volume of whole blood.
Isovolemia - Maintaining the same volume. In this situation, the volume of fluid in the body.
Sources:
Silverglied, Arthur, MD "Acute normovolemic intraoperative hemodilution" http://www.uptodate.com/
