Acute normovolemic hemodilution (ANH) is a blood conservation technique that entails the removal of blood from a patient shortly after induction of anesthesia, with maintenance of normovolemia using crystalloid and/or colloid replacement. The amount of blood removed varies between one and three units (450 to 500 mL constitutes one unit), although larger volumes may be withdrawn safely in certain circumstances. The blood is infused into the patient during or shortly after the surgical procedure.
ANH can be used as the sole blood conservation technique, or it can be combined with preoperative autologous donation (see "Surgical blood conservation: Preoperative autologous blood donation"), blood salvage (see "Surgical blood conservation: Intraoperative and postoperative blood salvage"), or both.
Whether ANH is effective in decreasing allogeneic blood transfusion is debatable, and outcome benefits have not been clearly demonstrated. (See 'Advantages and disadvantages' below.)
Acute normovolemic hemodilution (ANH) can be considered for patients with normal initial hemoglobin (Hgb) levels who are expected to lose more than two units of blood (900 to 1000 mL) during surgery. It is safest when used in healthy, young adults, but can be used in other populations. It is a good option for Jehovah's Witnesses who will consent to ANH if the blood is maintained in a closed circuit continuous flow system . (See "The approach to the patient who refuses blood transfusion".)
In patients with a normal or high initial Hgb levels who are undergoing cardiac surgery, decreased blood viscosity associated with the induced anemia may have cardioprotective effects [2,3].