Acute Normovolemic Hemodilution (ANH)
Also known to some as “isovolemic hemodilution,” ANH is, in short, collecting blood from a patient immediately before surgery (that’s the “acute” part), replacing the volume with IV fluid (that’s the “normovolemic hemodilution” part), then giving the blood back to the patient at or near the end of the surgery.
In ANH, multiple units of whole blood are withdrawn from a patient immediately before a surgical procedure, with immediate replacement of the patient’s blood volume, typically with normal saline.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 Near the end of the surgery, the withdrawn blood is re-infused (with the last units collected being the first units to go back in) and the patient’s blood volume is decreased through diuresis, as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 The units withdrawn must be labeled with the patient’s name, expiration time of the product (8 hours from time of collection if stored in the operating room, 24 hours if stored in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, ANH is elegant, cool, and makes lots of mathematical sense. It’s been shown to be of most benefit in cardiac surgery. 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 detailed or extensive on the benefits of ANH, especially in cases of only mild to moderate blood loss.
For much more on discussion on the practical use of ANH, see the June 2022 Blood Bank Guy Essentials Podcast with Dr. Steve Frank.
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