Transfusion Medicine: Current controversies
Adam Lancaster, DVM, DACVECC
The transfusion of blood products is common for many critically ill patients. While numerous studies in human medicine have identified “best practices” related to the administration of blood products, less is known in veterinary medicine. In this article we will focus on three controversies that exist regarding blood product administration including the existence of a “transfusion trigger,” the effect of storage lesions, and the best way to administer packed red blood cells (pRBC).
The “transfusion trigger” is the hematocrit (HCT) below which a transfusion should be administered. Significant controversy exists as to what level of HCT necessitates the administration of pRBC (or whole blood). Numerous studies in human medicine have shown equivocal or even increased mortality with a more liberal policy (transfusions were consistently given for more mild cases of anemia) compared to a more conservative transfusion policy. This is likely the case in our patients as well. Blood transfusions are not benign and may be harmful, yet may be life saving when used properly. No transfusion trigger has been identified in these studies and blood products should be given when clinical signs consistent with anemia are present. Correction of hypovolemia with fluids other than blood products may be sufficient in cases of hemorrhage.
Storage lesions are changes that occur within the blood products secondary to their storage. These include decreases in ATP and nitric oxide, increased RBC aggregation and increases in hydrogen ions, potassium (from RBC hemolysis), pro-inflammatory cytokines, histamine, complement and lipids. While these changes are known to occur, their ultimate impact on the patient is less clear. Some studies have shown increases in transfusion reactions or decreased survivability of transfused RBCs when older blood is administered compared to fresher blood. Other studies have not identified significant differences. Ultimately, fresh blood products are probably preferable to older products and should be administered when possible.
Recently, the technique used to administer pRBCs has come under scrutiny, specifically the use of syringe or fluid pumps for administration. A study performed on canine blood showed that RBC survivability was significantly decreased when a syringe or fluid pump was used compared to just hanging the unit and letting it run via gravity. This may have the effect of increasing transfusion reactions and necessitate additional blood product administration. This may be of particular importance in our patients due to the expense of blood products and potential for financial factors to influence our treatment.
These are a few current controversies related to transfusion medicine that are being discussed. Ultimately, as more information is made available we are better able to practice high quality, evidence-based medicine and improve the outcome of critically ill patients.