Controversies related to red blood cell transfusion in critically ill patients

Objective – To review the evolution of and controversies associated with allogenic blood transfusion in critically ill patients. Data sources – Veterinary and human literature review. Human Data Synthesis – RBC transfusion practices for ICU patients have come under scrutiny in the last 2 decades. Human trials have demonstrated relative tolerance to severe, euvolemic anemia and a significant outcome advantage following implementation of more restricted transfusion therapy. Investigators question the ability of RBCs stored longer than 2 weeks to improve tissue oxygenation, and theorize that both age and proinflammatory or immunomodulating effects of transfused cells may limit efficacy and contribute to increased patient morbidity and mortality. Also controversial is the ability of pre‐ and post‐storage leukoreduction of RBCs to mitigate adverse transfusion‐related events. Veterinary Data Synthesis – While there are several studies evaluating the transfusion trigger, the RBC storage lesion and transfusion‐related immunomodulation in experimental animal models, there is little research pertaining to clinical veterinary patients. Conclusions – RBC transfusion is unequivocally indicated for treatment of anemic hypoxia. However, critical hemoglobin or Hct below which all critically ill patients require transfusion has not been established and there are inherent risks associated with allogenic blood transfusion. Clinical trials designed to evaluate the effects of RBC age and leukoreduction on veterinary patient outcome are warranted. Implementation of evidence‐based transfusion guidelines and consideration of alternatives to allogenic blood transfusion are advisable.     

Acute normovolaemic haemodilution in a Clydesdale gelding prior to partial resection of the left ventral concha under general anaesthesia

A 16‐year‐old Clydesdale gelding underwent oral extraction of tooth 210 under standing sedation with partial resection of the left ventral concha under general anaesthesia 4 days later. Due to the highly vascular nature of the surgical site, significant intraoperative haemorrhage was anticipated. A lack of compatible donor horses confirmed by crossmatching prompted an autologous donation of 6 l of blood and acute normovolaemic haemodilution using a gelatine solution immediately prior to surgery. Intraoperative haemorrhage was estimated at 5% circulating volume and autologous transfusion was commenced once haemostasis was confirmed. The horse recovered uneventfully from general anaesthesia and surgery. To our knowledge this is the first report of acute normovolaemic haemodilution used in a clinical equine case.     

Canine and feline blood transfusions: controversies and recent advances in administration practices

ObjectivesTo discuss and review blood transfusion practices in dogs and cats including collection and storage of blood and administration of products. To report new developments, controversial practices, less conventional blood product administration techniques and where applicable, describe the relevance to anaesthetists and anaesthesia.Databases usedPubMed and Google Scholar using dog, cat, blood transfusion, packed red blood cells and whole blood as keywords.ConclusionsBlood transfusions improve oxygen carrying capacity and the clinical signs of anaemia. However there are numerous potential risks and complications possible with transfusions, which may outweigh their benefits. Storage of blood products has improved considerably over time but whilst extended storage times may improve their availability, a phenomenon known as the storage lesion has been identified which affects erythrocyte viability and survival. Leukoreduction involves removing leukocytes and platelets thereby preventing their release of cytokines and bioactive compounds which also contribute to storage lesions and certain transfusion reactions. Newer transfusion techniques are being explored such as cell salvage in surgical patients and subsequent autologous transfusion. Xenotransfusions, using blood and blood products between different species, provide an alternative to conventional blood products.     

Comparative stability of canine and feline hemostatic proteins in freeze‐thaw‐cycled fresh frozen plasma

Objective – To evaluate the stability of canine and feline hemostatic proteins in freeze‐thaw‐cycled (FTC) fresh frozen plasma (FFP). Design – Prospective study. Setting – Veterinary Teaching Hospital. Animals – Nine blood donor dogs and 10 blood donor cats. Interventions – Whole blood was collected and separated into packed RBC and plasma units according to standard methods. Each unit of plasma was divided into 2 equal aliquots and frozen (?41°C). One aliquot from each donor (FTC) was then thawed and then refrozen (?41°C) until time of analysis. The second aliquot (nonfreeze‐thaw‐cycled; NFTC) remained frozen until time of analysis. The hemostatic proteins assessed included coagulation factors, anticoagulant factors (antithrombin and Protein C), and adhesive proteins (fibrinogen and von Willebrand Factor). The coagulant activities of factors II, VII, VIII, IX, X, XI, and XII were measured in modified one‐stage activated partial thromboplastin time or prothrombin time assays. Antithrombin and Protein C activities were measured in chromogenic substrate assays. Clottable fibrinogen was measured via the Clauss method, and von Willebrand Factor concentration (vWF:Ag) was measured in an ELISA. A paired t‐test was utilized to identify differences in factor activity or concentration between FTC FFP and NFTC FFP. Measurements and Main results – No clinically or statistically significant differences (all P>0.05) were identified between FTC FFP and NFTC FFP. Conclusions – Refreezing FFP within 1 hour of initial thawing appeared to have no deleterious effects on the hemostatic protein activity or content of that unit. Transfusion of FTC FFP is expected to provide the recipient with comparable replacement of hemostatic proteins as FFP that has remained frozen.     

Evaluation of a rapid agglutination method for detection of equine red cell surface antigens (Ca and Aa) as part of pretransfusion testing

BACKGROUND: Blood typing before transfusion minimizes the risk of transfusion reactions and prevents immunization of the recipient against incompatible RBC antigens. The major RBC antigens that warrant identification before packed RBC or whole blood transfusions in horses are Ca and Aa. Standard blood-typing protocols are time-consuming (2.5-3.0 hours) and impractical in emergency settings. OBJECTIVES: The purpose of this study was to determine whether equine RBCs could be typed for Ca and Aa antigens using sera from horses with RBC antibodies in a modified rapid (15 minute) blood-typing protocol. METHODS: Serum was obtained from a horse with anti-Ca antibodies and from another horse with anti-Aa antibodies. The presence of agglutinating antibodies was confirmed with antibody screening. Venous blood samples, collected in citrate-phosphate-dextrose, were obtained from 21 horses of various breeds. Samples were blood typed in the Veterinary Medical Teaching Hospital Hematology Laboratory using standard methodology. Washed RBCs from each of the 21 horses were incubated individually with anti-Ca and anti-Aa sera at dilutions of 1:4, 1:8, and 1:16 for 15 and 30 minutes at room temperature and 37 degrees C. RESULTS: Of the 21 horses, 13 were identified as Aa+/Ca+, four were Aa+/Ca-, two were Aa-/Ca+, and two were Aa-/Ca-. All 17 Aa-positive horses had a positive agglutination reaction at all dilutions of anti-Aa serum, incubation times, and temperatures, while all Aa-negative horses were negative. Each Ca-positive horse had a positive agglutination reaction at all incubation time points and temperatures up to the 1:16 dilution of the anti-Ca serum. All Ca-negative horses were negative at all times, temperatures, and dilutions of anti-Ca serum. Use of the modified protocol on 26 hospitalized horses resulted in accurate typing, based on complete antibody screens. CONCLUSIONS: These results support the hypothesis that equine RBCs can be blood typed using a rapid (15 minute) protocol, at room temperature, for the presence of Ca and Aa antigens using equine-derived antisera. This technique may be beneficial for pretransfusion testing of equine patients in an emergency setting.     

Factor VIII inhibitors complicating treatment of postoperative bleeding in a dog with hemophilia A

Objective – To describe the clinical course of a dog with hemophilia A and circulating factor VIII inhibitors complicating the treatment of postoperative hemorrhage.
Case Summary – A 7-year-old castrated male Japanese Chin with hemophilia A, weighing 6 kg, was presented for dental cleaning, polishing, and extractions. Despite presurgical administration of cryoprecipitate, continuous oral bleeding occurred. Circulating factor VIII inhibitors were detected, and the postoperative hemorrhage was subsequently managed with extensive and prolonged blood component transfusion. The dog was discharged after a full clinical recovery.
New or Unique Information Provided – This case report describes the clinical consequences and successful treatment of postoperative hemorrhage in a dog with hemophilia A and circulating factor VIII inhibitors. A relevant discussion of the management of human patients with circulating factor VIII inhibitors is included.