Blood transfusion: Monitoring for adverse events (Proceedings)

Animals should be carefully monitored for any adverse reactions during and for several weeks following transfusion. Early recognition of transfusion reactions requires careful and frequent evaluation of the patient. Before infusion, baseline values of attitude, rectal temperature, pulse rate and quality, respiratory rate and character, mucous membrane color, capillary refill time, hematocrit, total plasma protein, and plasma and urine color should be monitored. The majority of these parameters should be checked every 30 minutes throughout the transfusion, and evaluated routinely post-transfusion to ensure the desired effect has been achieved (see Transfusion Monitoring Record).

Blood administration

Refrigerated blood may be gently warmed by allowing it to sit at room temperature for approximately 30 minutes. Properly administered cold blood will not increase the chance of a transfusion reaction, but, large amounts of cold blood given at a rapid rate can induce hypothermia and cardiac arrhythmias. Routine warming of red cell products is not recommended except in neonates, hypothermic patients, and with massive transfusion. Several types of blood warmers are commercially available, but are expensive. In an emergency situation, the tubing of the administration set can be placed in a warm water bath, not to exceed 37°C, so that warming can occur as blood passes through the tubing. The entire unit should not be immersed in the bath. Frozen products should also be thawed in a 37°C warm water bath. No blood product should be exposed to temperatures exceeding 42°C as this results in damage to red cells and denaturation of blood proteins. Warming red cell products or thawing plasma products in a microwave oven is not recommended.

Administration routes

Blood and blood components can be administered via many routes. Intravenous is obviously the most effective route in that the infused red blood cells or plasma products are immediately available to the general circulation. The intraosseous route is utilized in puppies or kittens when vascular access is difficult or unsuccessful. When delivering blood products intraosseously, infused cells and proteins are available to the general circulation within minutes. The most common sites for intraosseous catheter placement are the trochanteric fossa of the femur, the wing of the ilium and the shaft of the humerus. Care should be taken in the placement of these catheters due to the increased risk of osteomyelitis.

Administration volume

The appropriate volume of blood must be administered to each patient. Specific component therapy should be utilized to treat each disorder and the patient's cardiovascular status should always be assessed prior to determining the required volume and administration rate. The volume of blood administered is dependent on the presence of active bleeding, onset and degree of anemia, clinical status of the patient, and body weight. For practical purposes, feline patients initially receive one unit of whole blood (40-50 mL) or one unit of pRBC (20-25 mL) or one unit of fresh-frozen plasma (20-25 mL). Feline patients should be evaluated after each transfusion episode to determine if further blood product support is needed. The following dosages are used to estimate the blood component volume needed per transfusion episode in dogs:

• 20 ml/kg = ml WB needed

• 2 ml/kg WB will raise PCV by 1%

• 10 ml/kg = ml pRBC needed

• 1 ml/kg pRBC will raise PCV by 1%

• 6-10 ml/kg = ml plasma needed

Administration rates

Blood product administration rates are variable. The desirable rate of infusion depends upon the patient's blood volume, cardiac status, and hemodynamic condition. For example, a patient with massive hemorrhage may require a more rapid transfusion than a normovolemic patient with a chronic anemia. The maximum rate of transfusion for a normovolemic patient (where circulatory overload is a potential problem) is 11-22 ml/kg/hr, while hypovolemic patients can tolerate rates of 22-66 ml/kg/hr. If rapid transfusion is needed, blood can be infused as rapidly as the patient's circulatory system will tolerate, within a few minutes, if the rate does not cause the red cells to hemolyze. Cardiovascularly compromised animals cannot tolerate infusion rates that exceed 4ml/kg/hr. It is recommended for all patients that blood components be infused slowly (e.g., 1 ml/kg) for the first 10-15 minutes while closely observing for signs of an acute transfusion reaction. As a rule, the blood product should then be infused as quickly as will be tolerated, but should be completed within 4 hours to ensure administration of functional blood components and to prevent growth of bacteria in the event of contamination. Maximum time should not be confused with recommended time; most transfusions are completed within 2 hours. Most feline transfusions may be safely completed in 1 hour, with the exception of cats with heart failure.

All blood products should be filtered in order to help prevent thromboembolic complications. Standard blood infusion sets have in-line filters with a pore size of approximately 170-260 microns. A filter of this size will trap cells, cellular debris, and coagulated protein. Trapped debris combined with room temperature conditions may promote proliferation of any bacteria that may be present; therefore, blood infusion sets may be used for several units of blood products or for a maximum time of 4 hours. Micoraggregate filter systems with a pore size of 20-40 microns may be used for low-volume transfusion (i.e., <50 ml whole blood, <25 ml pRBC or plasma).

Transfusion reactions

Animals should be carefully monitored for any adverse reactions during and for several weeks following transfusion. Transfusion reactions can be classified as immune-mediated or nonimmune-mediated.

Immune-mediated transfusion reactions

Immune-mediated transfusion reactions can be hemolytic in origin, with either an acute (due to preexisting alloantibodies or prior sensitization) or delayed (can be exhibited > 4 days post transfusion) presentation. Hemolytic transfusion reactions are the most serious, but are less common. In acute situations, intravascular hemolysis is due to preexisting antibodies, as seen in the mismatched transfusion of feline type A blood to a cat with type B blood or in a previously sensitized DEA 1.1 negative dog receiving DEA 1.1 positive blood. Clinical signs include, but are not limited to, fever, tachycardia, weakness, muscle tremors, vomiting, collapse, hemoglobinemia and hemoglobinuria. Vomiting can be noted with any type of transfusion reaction; therefore, patients receiving blood products should not be fed during or just prior to transfusion.

Nonhemolytic transfusion reactions are a result of antibodies to white blood cells, platelets, or plasma proteins. Clinical signs include urticaria, pruritus and pyrexia. Present thinking attributes most febrile nonhemolytic reactions to the actions of cytokines, predominantly those produced by leukocytes in the transfused unit. These reactions are most often transient in nature and do not cause life threatening situations.

Nonimmune-mediated transfusion reactions

There are a variety of factors associated with nonimmune-mediated transfusion reactions. In order to avoid these reactions, careful attention should be given to the collection, processing, storage, and administration of all blood products.

Any type of trauma to the red blood cells will potentially cause hemolysis: 1) overheating red blood cell products (also will cause protein denaturation and may increase bacterial growth during infusion), 2) freezing red blood cell products, 3) mixing red blood cell products with nonisotonic solutions causing cellular damage, 4) warming and then rechilling blood products, and 5) collecting or infusing blood through small needles or catheters.

Bacterial pyrogens and sepsis can be a complication of improperly collected and stored blood. Dark brown to black supernatant plasma in stored blood indicates digested hemoglobin from bacterial growth. Any blood with discolored supernatant should be immediately discarded. Patients experiencing this complication will most often mount a febrile response 15-20 minutes from start of infusion.

Citrate intoxication may occur when the citrate/blood volume ratio is disproportionate or in massively transfused patients, particularly in patients with liver dysfunction. Common clinical signs include involuntary muscle tremors, cardiac arrhythmias, and decreased cardiac output. This compromised state can be confirmed by obtaining ionized serum calcium. If citrate toxicity is in question, blood administration should be discontinued and calcium gluconate administered.

Because blood is a colloid solution, vascular overload is a potential complication. Clinical signs include coughing (as a result of pulmonary edema), dyspnea, cyanosis, tachycardia, and vomiting. If volume overload is of concern, blood administration should, at the very least, be temporarily discontinued and supportive care instituted.