This experimental study describes a modified cardiopulmonary bypass circuit using a bovine hemoglobin solution priming that protects a portion of the autologous blood volume from the damaging effects of bypass.

– Philippe Van der Linden

The authors conducted an animal experiment to evaluate the efficacy of a novel double venous reservoir bypass circuit, used in conjunction with a polymerized hemoglobin prime solution, to sequester venous blood during cardiac surgery and improve hemostasis after the operation. The authors conclude that “net conservation of the platelet mass occurs, a portion of which is not exposed to the deleterious effects of hypothermia and cardiopulmonary bypass.”

Unfortunately, the study suffers from several limitations. First, the control group was managed with a standard cardiopulmonary bypass circuit, so it is difficult to know if the observed benefit could have been observed using only the novel equipment. Second, a very modest number of platelets were conserved, despite extreme hemodilution in both groups (dogs weighing 18-22 kg were bled 900 to 1000 mL and the circuit was primed with 2 L of lactated Ringer’s solution). As mentioned by the authors, they used an adult size oxygenator for a pediatric size model without cardiac disease. Thus, the model does not apply to the clinical situation. Platelet counts decreased much more than would be expected in humans (from 245,000/mm3 to 33,000/mm3 in the control group and 48,000/mm3 in the HBOC group). Finally, platelet function was not evaluated, nor was the importance of postoperative bleeding.

The only positive finding of the study was that cardiac function was better preserved after a period of cardioplegia when hemodilution was compensated with HBOC. Nonetheless, the study was terminated before separation from cardiopulmonary bypass, so the “clinical” significance of the improved cardiac indices remains elusive.

In summary, on the basis of this laboratory experiment, it is impossible to conclude that the double venous reservoir + HBOC technique is likely to decrease bleeding and transfusion requirements.

– Jean-Franois Hardy