Acute Normovolemic Hemodilution (ANH)

Also known as “isovolemic hemodilution,” this is a method of autologous perioperative blood collection. In ANH, multiple units of whole blood are withdrawn from a patient immediately before a surgical procedure, with immediate replacement of the patient’s blood volume, typically with normal saline. The idea is that the patient bleeds more dilute blood during the procedure, and the patient’s heart may pump more efficiently due to decreased blood viscosity. Near the end of the surgery, the withdrawn blood is re-infused (with the last units collected being the first units to go back in) and the patient’s blood volume is decreased through diuresis, as necessary. The units withdrawn must be labeled with the patient’s name, expiration time of the product (8 hours from time of collection if stored in the operating room, 24 hours if stored in the blood bank), and the statement, “For Autologous Use Only.”

In the proper hands, normovolemic hemodilution is elegant, cool, and makes lots of mathematical sense. So, why the heck isn’t it used all that often? First, performing ANH requires a knowledgeable operator (most commonly, an anesthesiologist) that understands how to collect donor blood, use the collection bags (with scales as applicable), and label the product. That combination doesn’t happen very often. Second, not enough clinicians even know about ANH, and fewer still consider it as an alternative to preoperative autologous blood collection. Finally, the data isn’t all that great on the benefits of ANH, especially in cases of only mild to moderate blood loss.

For more on discussion on the practical use of ANH and other methods in Patient Blood Management, see the March 2016 Blood Bank Guy Essentials Podcast discussion with Dr. Steve Frank on Bloodless Medicine.

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