To the Editor:—
We read with interest the recent article published by Casati et al. 1evaluating the use of acute normovolemic hemodilution (ANH) in adult cardiac surgery. In this study, the authors failed to demonstrate any beneficial effect of ANH on allogeneic blood requirements. However, this study evaluated the contribution of ANH as part of a blood conservation strategy rather than the efficacy of ANH itself. Indeed, the efficacy of ANH as a blood-saving technique is essentially related to a reduction of the net erythrocyte loss. Therefore, as shown by different mathematical analyses, the efficacy of the technique depends on the initial erythrocyte mass (which is related to the preoperative hematocrit and the circulating blood volume), the transfusion trigger (the hematocrit at which erythrocytes will be transfused), and most importantly, the perioperative blood losses. 2,3
In the study from Casati et al. , 1the baseline blood conservation approach aimed to markedly decrease perioperative blood losses by the use of cell-saving techniques and administration of tranexamic acid. In addition, the amount of blood harvested by ANH was quite low (500 ml) and returned to the patients before leaving the operating room. As a result, hematocrit at intensive care unit arrival was similar in the control and ANH groups. As postoperative blood losses were comparable in the ANH and the control groups, the net postoperative erythrocyte loss was similar in both groups. It is therefore not surprising that the use of limited ANH in such a blood conservation approach did not result in a decreased allogeneic blood requirement.
The demonstration of the efficacy of ANH as a blood conservation technique requires protocols that either avoid the concomitant use of other techniques decreasing perioperative blood loss or compare these techniques with ANH. Clearly, the adoption of a well defined blood conservation strategy results in a significant reduction in allogeneic blood requirements in cardiac surgery. 4,5The effectiveness of any blood conservation strategy depends on a careful cost-benefit analysis of the different techniques to be used in relation to the patient's limitations, the type of surgical procedures and techniques, and the health care environment.