Tolerance of Acute Anemia: The Anesthesiology Perspective

SUMMARY Anesthesiologists have to face anemia in a variety of surgical interventions and have had the challenge of assuring positive patient outcomes. As such, treatment of acute anemia has traditionally resulted in increased exposure to allogeneic blood transfusions. Enhancing our knowledge of the hemoglobin molecule, its functions and reserve, allows the anesthesiologist to utilize compensatory mechanisms to achieve a positive outcome, with the reduction or elimination of patient's exposure to allogeneic blood transfusions. Since the inception of anesthesiology as a medical specialty, one of the most important issues for anesthesiologists has been oxygen delivery and consumption. Anemia has been a long-time challenge for the anesthesiologist. Anemia is defined as a decline of hemoglobin concentration or hematocrit. During acute normovolemic anemia, compensatory mechanisms are elicited at both the macrocirculatory (systemic) and microcirculatory level. Acute normovolemic hemodilution (ANH) is the intentional dilution of blood (a state of anemia) caused by controlled withdrawal of surgical patient's blood for reinfusion within 8 hours during and following surgical blood loss. This technique provides fresh whole blood for transfusion and avoids the pitfalls of predonated blood. ANH is an iatrogenic condition where dilutional anemia is used to the advantage of a patient for blood conservation, i.e. as an alternative for allogeneic blood transfusion. The effects of ANH-induced anemia on various organ systems and functions are discussed in addition to the effect of anesthesia and anesthetic depth.