Canine and feline transfusion medicine (Proceedings)

Aug 01, 2009

Transfusion of blood products is a frequent necessity in small animal practice. Although potentially life-saving, this procedure does carry some inherent risk. To practice successful transfusion medicine the clinician must understand not only when and how to administer the appropriate blood product; but also how to collect and store these products to minimize the potential for an adverse outcome.

Blood components

The plethora of blood products, fractions, and concentrates now available for transfusion may seem confusing. However, it is rational to use a component wherever possible as this practice not only reduces the element of risk, but is also a more efficient use of valuable resources.

Canine transfusions are commonly provided as components; packed red blood cells (pRBCs) and fresh-frozen plasma (FFP). Each unit (~450 mL) of whole blood, if processed promptly, may be divided into 1 unit of pRBCs and 1 unit of FFP. Fresh frozen plasma represents plasma that has been separated and frozen within 6 hours of collection. It has a shelf-life of 1 year, after which it is stable for an additional 4 years as frozen plasma. Fresh frozen plasma may also be divided into cryoprecipitate and cryo-poor plasma. Cryoprecipitate contains increased concentrations of factor VIII, von Willebrand factor (vWF), and fibrinogen. Fresh whole blood may also be processed into platelet-rich plasma or platelet concentrates and typically has a half-life of 30-40 days.

Collecting blood for feline transfusions is inherently more challenging than for canine blood transfusions. Cats' blood volume is less than dogs' and donation typically requires sedation. Though cat blood transfusions are still commonly administered as whole blood, units can be separated into pRBCs and FFP components and are commercially available.

Blood banking

Blood products may be purchased from commercial blood banks or collected and processed in-house before emergent need. The once common practice of bleeding a staff member's personal dog or an in-house donor on an as-needed basis is not appropriate for most emergency practices because of time constraints and the manpower required.

In dogs, whole blood is collected into bags containing citrate–phosphate-dextrose–adenine (CPDA-1) as the anticoagulant preservative. These bags provide a closed system for collection and separation, which minimizes the opportunity for bacterial contamination. Each bag is designed to collect 450 mL. Sixty-three milliliters of anticoagulant is located in the main collection bag. The storage time for canine packed red blood cells (pRBCs) collected in CPDA-1 has been suggested to be 20 days. This short lifespan is not a problem when the product collected is immediately used, but it does present a significant problem when products are banked for later use. Additive solutions for the preservation of RBCs are available in closed-collection systems used in dogs. Both Adsol and Nutricel have been evaluated as additive solutions for canine pRBC storage. Adsol extended viability from 20 to 37 days, and Nutricel extended viability to 35 days.

Cat blood is most commonly collected into a syringe through a butterfly catheter. The anticoagulant must be added before collection. Anticoagulants used most commonly include acid–citrate–dextrose (ACD) and CPDA-1. The ACD and CPDA-1 are used at a ratio of 1 mL per 6-9 mL of whole blood. Typically, feline whole-blood units contain a total volume of 60 mL (7 mL of anticoagulant and 53 mL of whole blood).