Discover the crucial steps for safe and successful blood transfusions in veterinary practice.
If you’re like many general practitioners, you might scratch your head a bit when the need for a blood transfusion arises. Emergency and critical care veterinarians perform transfusions on a regular basis, but the inconsistent demand for transfusions in general practice means that most of us are “starting from scratch” whenever we must administer one.
When faced with a patient needing a transfusion, it’s never wrong to send them to a referral hospital. With some preparation and the right materials, however, you can easily perform blood transfusions in-house. Take some to familiarize yourself with the general principles behind blood transfusions, outlined below, and know that you can always look up specific details and equations when the need arises.
Blood Types: An Overview
Dogs have at least 12 different blood types, and we are still discovering new blood antigens through ongoing research. In transfusion medicine, however, the most important consideration is the DEA 1 (dog erythrocyte antigen 1) allele. Most dogs are DEA 1.1 positive; these dogs are recognized as universal recipients. A DEA 1.1 positive dog can typically receive any blood type for their first transfusion without risking a serious, life-threatening reaction. Dogs that are negative for DEA 1.1 and DEA 1.2 are considered universal donors, and their blood is unlikely to trigger an immune reaction in other first-time transfusion recipients.
Cats have three general blood types: A, B, and AB. (The Mik antigen also plays a role in feline blood types, but its clinical relevance is unknown.) Type A is the most common blood type in cats. Type B primarily occurs in purebreds, and Type AB blood is considered rare. In cats, there is no such thing as a universal donor; cats naturally form antibodies against blood antigens they lack, even without a history of exposure. Type A cats will react to Type B blood and Type B cats will react to Type A blood, although Type AB cats can often receive either blood type.
Blood Type Testing
Ideally, all of your blood donors should be blood typed and all your patients should have their blood type assessed before receiving a transfusion. While these tests can be performed at a reference laboratory, in-house blood typing cards can identify DEA 1.1 in dogs and differentiate between the three feline blood types (A, B, AB).
Blood typing is essential in cats, for both the donor and the recipient, due to the presence of naturally occurring antibodies.
In dogs, however, antibodies are not formed against other blood types until a patient has received a transfusion. Therefore, blood typing transfusion recipients are recommended but not as strictly required in dogs.
Crossmatching
Crossmatching is recommended for all patients, even those of known blood types, given the fact that we are still discovering new information about red blood cell (RBC) antigens. Crossmatching is especially essential when the donor or recipient’s blood type is unknown.
In dogs, however, it is often possible to safely perform a first-time transfusion without crossmatching in an emergency, provided certain conditions can be met. You may consider avoiding crossmatching if there is no suspicion of immune-mediated disease, no transfusion history, and the donor has confirmed DEA 1.1 negative blood. However, if the patient is not critical, it’s still recommended to perform a crossmatch to reduce the risk of reactions.
Crossmatching can be performed manually or with commercially available kits. A major crossmatch assesses the compatibility between recipient plasma and donor red blood cells (RBCs), while a minor crossmatch assesses the compatibility of the recipient RBCs and donor plasma. Agglutination or hemolysis in the major or minor crossmatch signals incompatibility and should prompt a search for a new donor.
Calculating Transfusion Volumes
Before performing a transfusion, you must determine how much blood your recipient will need. To do this, you must know the current packed cell volume (PCV) of both the donor and recipient. Next, perform the following calculation: Transfusion volume (mL) = (Desired PCV – Current PCV) / (Donor PCV) x recipient blood volume (ml/kg) x recipient weight (kg). This formula will allow you to determine how much blood is required to raise the recipient’s PCV to a desired level.
Next, you must determine how much blood your donor can safely provide. In general, you can remove up to 15% of an animal’s total blood volume without a need for replacement fluid therapy. A dog’s blood volume is estimated at 90 ml/kg, which means that you can remove approximately 13.5 mL/kg from a canine blood donor. A cat’s blood volume is estimated at 60 mL/kg, which means a cat can typically donate 9 mL/kg. Calculating your patient’s blood volume and multiplying that number by 0.15 allows you to determine how much blood the patient can donate before replacement fluid therapy is needed.
Once you have performed these calculations, you should know how much blood you will be collecting from your donor and transfusing into your recipient.
Blood Collection
Blood is collected from the jugular vein of a donor dog or cat, typically with the pet in lateral recumbency. Closed collection systems are preferred, to reduce the risk of bacterial contamination. However, a syringe (with the correct amount of anticoagulant added) can also be used when collecting small volumes of blood in cats or small puppies. If blood is collected in a syringe, it is acceptable to administer blood to the recipient directly from the syringe, using a syringe pump.
Transfusion Administration
Transfused blood should always be administered through a micropore filter, to avoid the introduction of debris and blood clots. Blood should be kept cool, to reduce bacterial growth, but the administration lines can be run through a warm water bath for the patient’s comfort.
Transfusions should be started at a slow rate, to allow for the early detection of reactions. Begin the transfusion at a rate of 0.5 mL/kg/hr for the first 15-30 minutes, while carefully monitoring for signs of a reaction. Then, if all is going well, increase the administration rate to 1 mL/kg/hr. Once the patient has been receiving blood at a slow rate for a total of one hour, you can increase your desired administration rate.
Patients should be monitored closely during a transfusion, with attention given to the patient’s attitude, mucous membrane color, capillary refill time, temperature, pulse, and respiration. Any sign of a transfusion reaction should prompt an immediate cessation of the transfusion and additional treatments as indicated.
Transfusion Reactions
Acute immune-mediated transfusion reactions are rare but serious. Early signs may include fever, vomiting, tachycardia, tachypnea, weakness, and tremors.
Delayed immune-mediated transfusion reactions result in hemolysis. This means that the transfused RBCs do not last as long as expected and the patient’s PCV begins to fall in the days or weeks immediately after the transfusion.
Non-immune-medicated transfusion reactions may also occur. These reactions may be caused by volume overload, bacterial contamination, or citrate toxicosis (especially in dogs with liver disease). Signs of these reactions may vary, depending on the underlying cause and the patient’s overall health status.
Summary
While there are many steps involved in correctly performing a blood transfusion, this procedure does not have to be complicated. Before performing a transfusion, remember to assess blood types, perform crossmatching, and calculate your desired transfusion volume. Once these preparations are complete, you can collect blood from your donor and administer it to your recipient, with careful monitoring. Taking the time to think through these steps carefully can increase your comfort level and success with blood transfusions in general veterinary practice.
