Practical transfusion medicine (Proceedings)

Unfortunately, transfusion medicine tends to be a “right now” type of problem – the patient is unable to wait while blood or blood products are ordered and shipped to the practice. After a general review of blood products, the majority of this lecture is intended for the practitioner who does not have a blood bank at their hospital.

Components of Transfusion Therapy

Red blood cells:

The average canine red blood cell has a life span of 120 days, and slightly less for the cat (60-120 days, depending on reference). Red blood cells are present in many products, including fresh whole blood (FWB), whole blood (WB) and packed red blood cells (pRBCs). The life span for transfused red blood cells is shorter than for normal red blood cells, but there is no consensus on how long these products last. The dose of RBCs depends on the product. Whole blood products are dosed at 2 ml/kg (or 1 ml/pound) to increase the PCV by 1%. pRBCs are dosed at 1 ml/kg to increase PCV by 1%. The goal is NOT to transfuse to a normal PCV, but to transfuse to normalization of clinical signs. The clinical condition of the patient should dictate transfusions, rather than a number. A patient who rapidly goes from a PCV of 45% to 20% will be sicker than a patient who is chronically at a PCV of 17%.Tachycardia, elevated lactate, severe lethargy, ST segment depression or other signs of tissue hypoxia should guide transfusion. I typically aim to increase the PCV by 5-10%, and then reassess the patient to determine if additional RBCs are needed.

Clotting factors

Plasma contains many protein components. These include the clotting factors (stable and labile), von Willebrand factor (vWF) and fibrinogen (factor I). The products that contain clotting factors are FWB (all factors), FFP (all factors), FP (stable only) and cryoprecipitate (FVIII only). The vitamin-K dependent clotting factors (II, VII, IX, and X) are considered stable factors, whereas factors V and VIII are labile factors, meaning that their amounts decrease with storage. The most common reason for coagulopathy in veterinary medicine is anti-coagulant rodenticide toxicity (ACR). This can be treated with any product except for cryoprecipitate. If the cause of the clotting disorder is unknown, FFP is the best treatment. The dose of plasma (either fresh or frozen) to improve clotting times is 10-15 ml/kg repeated as needed until PT and aPTT have normalized. If FWB is used for this purpose, the dose must be doubled as the plasma fraction is roughly ½ of the amount transfused. There is significant debate over when clotting times need to be corrected. A rough rule of thumb is that if the patient is bleeding or at high risk of bleeding (clotting times significantly prolonged, invasive procedure), then transfusions should be given.

Albumin

Unfortunately, transfusions are a very poor way of increasing albumin levels. To increase albumin by 1.0 g/dl, approximately 40 ml/kg of plasma must be given. Each unit of plasma can be 125-250 ml/unit, depending on the source of the unit. This makes plasma transfusions impractical and expensive for most patients. Albumin distributes through the entire extracellular fluid compartment, not just the intravascular volume. Therefore, very large amounts must be given. Human albumin is a more efficient method of increasing albumin, although significant debate exists about its safety in veterinary patients. The best way to increase albumin is to ensure an adequate nutritional plan.

Platelets

Platelets are by far the most difficult blood component to transfuse. FWB, platelet-rich plasma (PRP) and lyophilized platelet (LP) products are available. Remember that regular plasma does NOT contain platelets are they are unable to survive either refrigeration or freezing unless special precautions are taken. While both PRP and LP contain active platelets, there is no information on how long those platelets are active once they are transfused. There is no information available on the longevity or activity of platelets in FWB.

Von Willebrand Factor

vWF is a multimer that is carried in circulation by Factor VIII, and functions in platelet activation and aggregation. Additional stores of vWF are released by platelets and vascular endothelium during coagulation. von Willebrands Disease (vWD) is a decreased amount of circulating vWF, and is manifested as bleeding tendencies. Sources of vWF are FFP, FWB, and cryoprecipitate. Lyophilized cryoprecipitate is available as well, although care must be taken to order the appropriate size. Some vials are made from 125ml plasma, while others are made from 250ml plasma. The dose of FFP or FWB is the same as for correction of clotting factor disorders. The dose of cryoprecipitate is 1 unit per 5-10kg, again depending on the size of the plasma vial from which it is made.

What to do if you don't have a blood bank

Donor selection

If a blood bank is not immediately available, your practice will rely on use of donor animals, and you will use fresh whole blood for the majority of your patients. Prior to use of ANY animal for blood donation, consider the following:

Dogs

Donor dogs should be ideally large (30-50 kg), young (between 1-7 year old), and tolerant of restraint. They should be screened before blood collection to be DEA 1.1 and 1.2 negative, healthy and transmissible-disease free (Ehrlichia canis/platys, Brucella canis, Babesia canis, and Dirofilaria immitis). At a minimum, they should be heartworm negative and on year-round prevention.

Cats

Donor cats should be at least 5 kg, young, indoors, vaccinated and negative for FeLV and FIV. Similar to dogs, a blood type, complete blood cell count and chemistry panel should be done prior to enrollment as a donor. In addition they should have no signs or symptoms of Feline Infectious Peritonitis, and ideally have a low titer. Preferably they should live in a low risk environment for all infectious feline disease (indoor only small population households).

Drawing and storing blood

Ideally, a peripheral catheter should be inserted after the donor has been sedated (if required) and replacement intravenous crystalloids administered (three times the volume of blood withdrawn can be administered over 20-30 minutes) after the donation is complete. Dogs can be sedated with opioids or opioid/ benzodiazepine combinations. Cats can be sedated with ketamine/diazepam for the procedure, or can be given alpha-2 agonists (bradycardia may require reversal agents). Dogs can be collected using the standard 16-ga needle connected to the transfusion pack by gravity, or by vacuum assistance. Cats can be collected using a butterfly catheter and 60ml syringe. Do not allow air to enter the collection system through the needle after completion of the transfusion. The system must remain closed to potential contamination. All blood collected to be used as stored components should be collected into CPDA-1 at a rate of 13-14 ml anticoagulant to 100 ml of blood. Blood collected for immediate transfusion can be collected into ACD. The actual collection should be done in an aseptic manner (i.e. shave, sterile prep, wear sterile gloves).

How much blood can be removed from a donor? Up to 15% of the blood volume can be removed safely, and up to 20% can be removed if followed by fluid therapy. Removal of 30% of blood volume will produce signs of hypovolemic shock. The blood volume of the dog is ~90 ml/kg and the blood volume of the cat is ~60 ml/kg. Therefore, the dog can have 13.5 ml/kg and the cat can have 40-50ml TOTAL removed safely.

FWB should be used within 4 hours of removal. WB can be stored in the refrigerator at 4-6ºC after collection. Red cell life is 35 days with CPDA-1. Blood can also be sedimented and the plasma component stored in the freezer. If you plan to separate blood, special collection systems should be used so that the system is not opened and exposed to air.

In-house blood typing and cross-matching

If typing cards are available, these should always be used prior to blood transfusion (and only for products containing RBCs unless prior plasma transfusions have resulted in reactions). Ideally, the blood type of the donor is known in advance. If your practice does not have blood typing cards available, skip to the cross-matching portion of this section.

Canine blood types and typing

DEA 1.1/1.2 negative is considered the universal donor. Typing cards check only for DEA 1.1; one of the most important antigens, but not the only antigen that can cause transfusion reactions. The presence of agglutination in the “Patient Test” well indicates that the patient is EITHER DEA 1.1 positive or is auto-agglutinating. Dogs who are auto-agglutinating should always receive 1.1 negative blood, because the typing cards are difficult to interpret when autoagglutination is present. Bitches which have whelped and any dog that has had a prior transfusion (> 7 days previous) should have a crossmatch performed prior to transfusion. One rule of thumb is that all dogs should be able to receive one blood transfusion without a reaction.

Feline blood types and typing

Typing felines prior to transfusion is mandatory. Type B blood is rarely stored, but ideally, a B cat should be available to the practice to donate as needed (Rex breeds, British Shorthairs, Maine Coons etc). Type A red cells given to a B cat are catastrophic, and Type B given to a Type A cat can occasionally cause a severe reaction. On the feline blood typing card, RBCs from type A cats will agglutinate with anti-A monoclonal antibodies and RBCs from type B cats will agglutinate with anti-B solution. Erythrocytes from type AB cats will agglutinate with both anti-A and anti-B reagents. The third well on the card serves as the auto-agglutination saline screen and must be negative in order to interpret results.

Rapid cross-matching

If blood typing equipment is not available, then a rapid cross-match is the easiest way to determine if recipient and donor are compatible. These are not as complex or as complete as the cross-matching performed in referral laboratories, but will be sufficient if time is of the essence. This is only required for transfusions containing RBCs. It requires an EDTA sample (purple top) from both the recipient and donor animals.

Centrifuge both samples (1000 x g for 5 min) to separate plasma from the RBCs.

Remove the plasma from each sample with a pipette, and transfer the plasma to a clean, labeled glass or plastic tube. Note any hemolysis.

Major cross-match:

Mix 1 drop donor RBC with 2 drops recipient plasma on a glass slide using a pipette.

Mix by slowly rocking the slide for several minutes.

Inspect for appearance of agglutination both visually.

Place a glass coverslip and inspect for appearance of microagglutination.

If there appears to be microagglutination, use the saline dispersion test (below) to determine if true agglutination is present.

Minor crossmatch: Repeat as above, but use 2 drops donor plasma and 1 drop recipient RBCs

Saline dispersion: Place one drop of saline immediately next to the coverslip. As the saline wicks under the coverslip, the RBC clusters should break up if only rouleaux is present.

The presence of agglutination (macro- or micro-) signifies incompatibility.

Transfusion protocol

All red cell products should be administered through a blood administration filter. A baseline TPR and PCV/TS should be collected prior to beginning a transfusion. Initial rate of administration should be slow (0.25-1 mL/kg/hr) for 15-20 minutes to monitor for transfusion reaction. Vital parameters (TPR) should be monitored every 15-30 minutes for the 1st hour, and then every hour until transfusion is completed. The calculated dose of red blood cell product should be administered within 4 hours of puncturing the donation bag. Total daily doses of red blood cell products should not exceed 22 mL/kg/day, unless severe ongoing losses are occurring (do not exceed 22 mL/kg/hr unless massive hemorrhage). If risk of volume overload is present, then maximum administration rate should be 4 mL/kg/hour. Patients who are experiencing severe and rapid blood loss should be administered red blood cell products as rapidly as needed to maintain adequate circulating volumes. Slow initial rates of transfusion are usually not employed in emergency situations. For example, the actively bleeding ACR patient should have the full dose of FWB or FFP within 20-30 minutes. A PCV/TS should always be performed within 60-90 minutes after completion of the transfusion to determine response.

Transfusion reactions

Type I – Allergic/Anaphylactic reaction

This is the most common transfusion reaction and is manifested by urticaria, pruritus, or fever. Anaphylaxis can occur, but is rare. Most of the time, the reaction is directed against an incompatible antigen located on the platelet or white blood cell remnants or some plasma protein component. If urticaria or fever is the only manifestation, the transfusion should be stopped temporarily, and diphenhydramine (2 mg/kg IM) administered. The transfusion can be reattempted after 20-30 minutes. If the fever or urticaria does not resolve within 30 minutes, Dexamethasone SP 0.25 mg/kg IV can be administered. Anaphylaxis should be treated with aggressive fluid resuscitation and antihistamines as described above if severe. Epinephrine (0.1 mL/kg or 1:100000 concentration IV) may also be necessary if severe bronchoconstriction and cardiovascular collapse are present. Restarting the transfusion is not recommended in this case.

Type ii – acute immunologic – hemolytic reaction

Acute intravascular hemolysis is the most severe of the transfusion reactions and results in hemoglobinemia and hemoglobinuria. Signs may include restlessness, anxiety, nausea, muscle tremors, urticaria, fever, tachycardia, tachypnea, and seizures. Acute death, thromboembolic disease, or acute renal failure are possible. The most common situations where this would occur include Type A blood to a B cat, or DEA 1.1 positive blood to a negative dog previously sensitized through previous transfusion or breeding (negative female dog bred to positive male with exposure to positive fetal blood during whelping). The transfusion should be discontinued immediately. IV fluid therapy is always indicated to support glomerular filtration rates and renal blood flow. Administration of corticosteroids (Dex SP 0.25mg/kg IV) may be beneficial.

Delayed immunologic reactions

This transfusion reaction is uncommon in veterinary medicine. Rapid destruction of transfused RBC is the most common reaction in this category.  Typically, DEA 3/5/7 antigen antibody reactions are involved through previous sensitization, or naturally occurring antibodies. Rapid drop in PCV within 3-7 days and evidence of extravascular hemolysis are the typical signs.

Acute non-immunologic

The most common problems associated with this category of reaction include vascular overload (cough, pulmonary edema, vomiting, urticaria, and serous nasal discharge). In addition, poor component handling can result in hemolysis (physical trauma to red cells during collection or administration, prolonged or inadequate storage, freezing, overheating, and mixing with non-isotonic fluids). If RBC damage is severe, then signs may similar to acute severe intravascular hemolysis, but more commonly reflect rapid transfused RBC destruction and extravascular hemolysis. Occasionally a pyrogenic substance from the plastic bag or tubing can cause a febrile response which is not immune mediated. Administration of RBC or plasma products with calcium containing crystalloids (LRS) can cause microembolization within the IV tubing to occur. Inappropriate plasma product storage or administration can result in poor viability of plasma/clotting proteins and ineffective response. Massive transfusion in severe/ catastrophic hemorrhage can result in hypocalcemia and/or anticoagulant toxicity. This is seldom encountered in veterinary medicine. Disease transmission can also occur if donors have not been carefully chosen and screened.