Revisiting acute normovolemic hemodilution and blood transfusion during pediatric cardiac surgery: a prospective observational study.

Children undergoing cardiac surgery with cardiopulmonary bypass (CPB) are at high risk of being exposed to relatively large volumes of allogeneic blood products. If blood transfusion can be life-saving in some circumstances (e.g. major haemodilution or massive haemorrhage), the administration of large volumes of allogeneic blood products has been shown to significantly increase the risk of postoperative complications. Over the last decades, different strategies have been developed to reduce the need for blood product transfusions.

Acute normovolemic hemodilution (ANH) has been used for a long time in adults undergoing high bleeding risk procedures, including cardiac surgery. While some studies reported a decrease in the incidence of transfusion and in the volume of red blood cells transfused, only limited evidence exists in infants and children undergoing cardiac surgery. Major differences exist between children and adults undergoing cardiac surgery, limiting the use of ANH to a small number of infants and children. On the one hand, the circulating blood volume and the degree of haemodilution generated at initiation of CPB is significantly higher in infants and young children, than older kids and adults. On the other hand, many infants and children will come to surgery with a certain degree of anemia, which will not allow the haematocrit to be maintained above 24% after cardioplegia and the use of a blood-free strategy. Finally, if ANH aims to reduce the risk of coagulopathy and platelet dysfunction, and to transfuse cytokine-free blood, storage of blood under suboptimal conditions, for a sometimes long and unpredictable period, may also impair the quality of the whole blood retransfused. For those reasons, the benefit and risk of ANH in infants and children undergoing cardiac surgery should be carefully assessed.

In this study, Sebastian et al. assessed the effect of blood collection (e.g. syringe vs. bag) on platelet count and function. As secondary objectives, the authors looked at perioperative blood transfusions and outcomes associated with ANH. The study was performed on a small and heterogeneous population, including ‘children’ with ages ranging from 3.1 to 15.4 years old, and only 18% of whom had a cyanotic heart disease. The authors conclude that ANH protects platelets from the effects of CPB and offers an important autologous blood product that improves haemostasis after surgery. Platelet count and function are preserved regardless of the method of collection or the length of storage.

ANH appears to be an effective strategy to reduce the need for allogeneic blood product transfusion; howeber, only a small number of infants and children should be considered as good candidates and would benefit from ANH. Even though the authors reported positive results, the study population represents a minority of patients undergoing cardiac surgery. In conclusion, if ANH can be considered as an effective strategy to reduce allogeneic blood product transfusion, the benefits and the risks of applying this technique to infants and children undergoing cardiac surgery should be carefully weighted.

– Dave Faraoni