Polymerized bovine hemoglobin solution as a replacement for allogeneic red blood cell transfusion after cardiac surgery: results of a randomized, double-blind trial.

The article by Jerrold Levy et al. is one of the few randomized controlled trials published on the use of hemoglobin-based oxygen-carrying (HBOC) solutions in patients. Similarly to the study by Lamy et al. on the use of diaspirin cross-linked hemoglobin published in Anesthesiology in 2000, HBOC-201 was used for the initial treatment of anemia in patients after cardiac surgery requiring cardiopulmonary bypass. The authors showed that, in these patients with a hemoglobin concentration ranging between 6.0 and 9.0 g/dL, the use of HBOC-201 avoided the transfusion of red blood cells (RBC) in 34% of patients and reduced the subsequent use of RBC by a little less than half a unit per patient (P = 0.05). Blood bank requirements were reduced from 105 units in the group treated initially with RBC to 91 units in the group treated initially with HBOC-201. Mean arterial pressure increased and cardiac index decreased significantly after infusion of the HBOC solution but oxygen delivery was similar between the groups.

What can clinicians conclude from this study?

First, the blood savings achieved in this context are modest and of marginal importance (both for patients and for the blood bank) in light of the substantial amounts of HBOC-201 required. One should remember that only anemic patients were enrolled: the blood sparing effect for the entire population would, consequently, be even smaller.
Second, blood savings were achieved at the expense of significant side effects (increased blood pressure, decreased cardiac index and jaundice), as in the study by Lamy et al.
Third, hemoglobin concentrations were similar in all patients at day 6 after surgery. Although a hematinic effect of HBOC-201 is invoked, no data are presented to support this hypothesis. One could also argue that restoration of a normal fluid balance and elimination of the hemodilution observed commonly after cardiopulmonary bypass may be responsible for the rise in hemoglobin concentration. Tolerance of a low transfusion threshold might have resulted in similar blood savings.

HBOC solutions are an interesting concept but the products available at this time present several limitations. Their effect is short-lived because they have a short plasma half-life and are rapidly oxidized to methemoglobin. In addition, their use is associated with clinically significant adverse events while the benefits demonstrated in controlled trials remain modest. Finally, the cost of HBOC-201 remains unknown and may further limit the use of this alternative to transfusions.

– J.-F. Hardy.